Updates on the Classic 30 mods?

[BobW]

Steve, et al, I applied the tone cap changes (orange drops) about 18 months ago, and liked the changes. It was a great improvement, but was wondering if anything new has been discussed to further improve the tone? Am not completely happy with the lead channel, it's still a little too gritty at the top end. Has anyone tried any *umble type mods? increasing the Rp, adjusting the coupling caps, etc? I may try Ray Ivers suggestion using zeners to clamp the large negative grid swing.

[Ray Ivers]

Bob,

If you're thinking of trying the Zener thing on the preamp tubes (and hopefully reporting back with some intel) that would be outstanding - I only tried it on the power stage, but it should also work on the preamp tubes.

Ray

[BobW]

Ray,

I plan to give it a try hopefully later in the week after the usual fires on Monday and Tuesday mornings. It would be best to look at the nominal signal gain w/scope to determine a ballpark Vz in the preamp section. My bassman *umble is a good test candidate since it's easily accessible.

[Joe N]

Originally Posted by BobW

Steve, et al, I applied the tone cap changes (orange drops) about 18 months ago, and liked the changes. It was a great improvement, but was wondering if anything new has been discussed to further improve the tone? Am not completely happy with the lead channel, it's still a little too gritty at the top end. Has anyone tried any *umble type mods? increasing the Rp, adjusting the coupling caps, etc? I may try Ray Ivers suggestion using zeners to clamp the large negative grid swing.

you can replace c4 (470pf) with a higher value like .002, .0047, etc... and that will allow more lows through, but I wouldn't go to high or it will be really loose sounding. you can do the same with c4, but can go higher to .022uf if you want. you can clip c1, which is an ice picky JCM800 like trble peaking cap, or replace it with a higher value like .002, which will sculpt your lower mids. lowering the 150k RP's to 100k will help too. thats a start

[BobW]

Joe, I appreciate your comments, but gather you have not performed any particular component value changes in this amp? The reason why I'm asking is because this amp (Classic 30) is used mostly as my alternate amp in smaller clubs. I can try a few changes by trial and error, but am mostly interested in proven changes someone has already tried. This amp is not the easiest to tweak and reassemble w/o chassis buzzes, etc. I have already tried a few gain stage changes, added snubbers to tame the icepick highs, and may just leave it at that. thanks for the suggestions.

[Joe N]

Originally Posted by BobW

Joe, I appreciate your comments, but gather you have not performed any particular component value changes in this amp? The reason why I'm asking is because this amp (Classic 30) is used mostly as my alternate amp in smaller clubs. I can try a few changes by trial and error, but am mostly interested in proven changes someone has already tried. This amp is not the easiest to tweak and reassemble w/o chassis buzzes, etc. I have already tried a few gain stage changes, added snubbers to tame the icepick highs, and may just leave it at that. thanks for the suggestions.

not particulary the classic models, but have done extensive mods on 5150's which are assembled the same, and a heap load of other high gainers, low gainers, and everything in between etc for years.... So I do have alot of working experience under my belt, and I know the math behind what does what and most complaints of fizzy, ear piercing gain are a result of a few key things, not always, but mostly. sometimes the OT, will greatly improve things, sometimes it wont. The truth of the matter is somebody can tell you that x mod gives you y result, but you really don't know unless you sniff solder. in your case you may just need high bandwidth restriction. snubbers work, but I would use grid stoppers instead if at all possible. not only can you roll off the highend, but you have the added bonus of preventing blocking distortion. Point is Sniff some solder, find out for yourself.
Joe N

[Joe N]

another good tip if you are tweaking a pcb amp, but don't want to take it apart is to cut out the components so that there is still a bit of the lead still sticking out of the solder pads, and then solder the new components to those from the top of the board. that way you can tweak, then take it apart when you finalize the changes. just another idea

[Ray Ivers]

BobW,

I have modded several Classic 30's, but none recently... if you want to greatly reduce raspiness on the overdrive channel, that shouldn't be too difficult to accomplish, but I agree that it would be best to have a concrete idea of at least what frequency response you want before pulling the chassis. If you had a good EQ to throw in the loop for testing purposes, that would wonderful IMO - you can determine the exact HF break point that sounds best to you, then do the math, open 'er up, and start changing out components to the values indicated by your calculations.

FWIW, reducing the value of R13, increasing C16, and adding a small-value cap across R3 are what I would be looking at, just at a glance; these mods would reduce overdrive-channel 'fizz' without affecting the other channel. If C16 and the new cap across R3 are sized to work together, the reduction in grit can be quite dramatic, while leaving the desirable treble frequencies mostly intact.

Does this amp really have a 470pF cap (C7) to ground after the VR2 gain control? If you need all your pickups to sound like neck pickups, this is definitely the way to go...

Ray

[Enzo]

And don't overlook something simple like putting a 5751 in V2 in place of the 12AX7.

[BobW]

Ray, Much appreciated for the suggestions thanks will give them a try. I had previously lowered R13 to 8.2k, which gives about a 1.3kHz rolloff. Are you talking about R3 or VR3? I had tried a snubber (.0012uf cer and a 250k pot) at V2-6/R3 node to ground to dial out the fizz, but it took too much off the top end as well. I could also try a small value cap across VR3 to act as a LPF.

Thanks Enzo, I don't have any 5751s at the moment, but may try a 12AY7 when I get back from TDY. thanks

JoeN, I thanked you for your input and also happen to have a LOT of amp repair/design experience. 15 yrs. as a military tech + 16 yrs as an electrical engineer, with most of my spare time over the years as a repair tech for two local music stores qualifies as a 'lot'. The initial post wasn't meant to be a pissing contest. I was simply asking was for proven suggestions to help the tone. As I said, this is a secondary amp that I don't want to spend a lot of time on. I have other priority amp work.

"Point is Sniff some solder, find out for yourself."
This comment was unecessary and not appreciated.

Something to consider, next time when someone asks for suggestions on a proven tweak or mod it won't always mean that person doesn't know what end of the soldering iron to hold.
Enough said. peace

[Ray Ivers]

BobW,

I guess I really should have said "jumper R13"; IMO a shelving response is not what's needed here, but rather a full-on roll-off (hey, that's kind of a neat expression) increasing up the frequency spectrum.

I meant putting a very small-value cap - maybe 220pF or so, much smaller than your 1200pF - across R3, in conjunction with another cap across VR3 (C16) achieving the identical rolloff characteristics as the across-R3 cap - that's what I meant about "doing the math", the values would have to be worked out in advance to achieve the desired 12dB/octave rolloff. IME this is nearly impossible to do by ear; you may end up with something you like the sound of, but it's unlikely to be a true 12dB/octave filter, which I feel is the best starting place for tweaking (rather than starting from a complete unknown and hoping for the best, especially on a difficult-to-tweak design you hope to get right the first time). IME one cap won't do the job - using a big-enough value to reduce the fizz also removes treble, as you found out.

Ray

[Joe N]

Originally Posted by BobW

Ray, Much appreciated for the suggestions thanks will give them a try. I had previously lowered R13 to 8.2k, which gives about a 1.3kHz rolloff. Are you talking about R3 or VR3? I had tried a snubber (.0012uf cer and a 250k pot) at V2-6/R3 node to ground to dial out the fizz, but it took too much off the top end as well. I could also try a small value cap across VR3 to act as a LPF.

Thanks Enzo, I don't have any 5751s at the moment, but may try a 12AY7 when I get back from TDY. thanks

JoeN, I thanked you for your input and also happen to have a LOT of amp repair/design experience. 15 yrs. as a military tech + 16 yrs as an electrical engineer, with most of my spare time over the years as a repair tech for two local music stores qualifies as a 'lot'. The initial post wasn't meant to be a pissing contest. I was simply asking was for proven suggestions to help the tone. As I said, this is a secondary amp that I don't want to spend a lot of time on. I have other priority amp work.

"Point is Sniff some solder, find out for yourself."
This comment was unecessary and not appreciated.

Something to consider, next time when someone asks for suggestions on a proven tweak or mod it won't always mean that person doesn't know what end of the soldering iron to hold.
Enough said. peace

The sniff solder comment wasn't meant to be undermining, and I don't know how it could have been mistaken for such. maybe it wasn't worded clearly, but my point was that you can figure out on paper what freq. you want to kill, and where you want to kill it, but you wont know if you like the change until you actually do it. sniff some solder to me means, the only way to really know is to do it. I cant remember how many times I have asked Trace Allen for specific modding help, and while sometimes he gave specifics, sniff some solder is the best advice anyone has ever given me. I didn't assume anything about you, I was actually trying to be very helpful. I'm sorry if you mistook my comment for something that was mean spirited or degrading, It surely wasn't meant to be

[daz]

This is a favorite subject of mine. I've had 4 of them and i'll tell you what i've done and the results. I feel like a broken record because i've mentioned this at various forums a million times, but the way my C30 sounds i just want to let anyone who might be thinking about it know. I did a number of steves mods, or i should say mods posted at his site. Not sure which are and aren't his. But in any case, there are 3 mods that i found work and work great. the rest i changed back to stock because they either didn't sound good or weren't my taste. I like a vintage sound without any low end flab and a master with a bit of gain. Not a lot, but enough to play any classic rock and blues.

The first mod i'll mention because i felt it was a huge improvment was to cathode bias the amp. It's actually a very simple mod. there's a gif schematic on steves site that shows the changes, but enzo recommends one difference that i found to be better......a 100 ohm cathode resistor instead of the recommended 60 ohm. This mod really opens the amps tone up and makes it transparent and much more pure and organic like a simple tube amp. the next was the C4 swap as mentioned. The mods recommend a 680 or 820 PF cap, and i found the 620 worked much better. It helps the lead channel a lot and drops the gain down a bit. the processed nasally sound is gone. The last was the input where i simplified it to a classic fender or marshall input. theres loads of garbage there that i think caused the amp to not take pedals very well.

The result is nite and day. every complaint i've ever heard about this amps tone is gone, and i'm not exaggerating. the tone is full and real/organic and so much better than stock it's not funny. The only thing that keeps it from being squarley in the high end boutique relm is the harmonic content. It's actually very good, but not at the level i've heard in some of the boutique stuff. But i did compare it to a number of boutiqe amps one day at the local high end shop and i honestly preferred the C30. It wasn't as good in some areas, but the overall tone is now so much better that it's competitive with many generally desirable amps that cost much more. I also put in a presence and a pot in place of the boost to allow it to be variable. (very cool mod !)

Anyways, these mods are the ones that survived my taste test. to give you an idea of the tone i like, i love marshalls from the 800's on down and my preference for tone and the way to get it is the typical SRV "volume control as tone/gain control" ........amp in OD mode and the volume to clean up. In this context it's just beautiful.

[Enzo]

If you look at the input of the stock C30, the series cap C8 is a huge .1, that should be fairly transparent to any freqs we might care about, but it blocks DC. I sure would not want to guarantee anyone that they will not have pedals with some DC offset at the output.

The shunt cap C10 is a small 39pf. Its purpose is to prevent RF from entering the amp - the old my amp picks up radio stations condition. 39pf oight not the roll off highs you care about much, but if so, then replace it with a 22 or an 18. I like the protection. I can test this stuff too, since there is an AM transmitter a half mile away. This is a high RF environment here.

[daz]

Originally Posted by Enzo

If you look at the input of the stock C30, the series cap C8 is a huge .1, that should be fairly transparent to any freqs we might care about, but it blocks DC. I sure would not want to guarantee anyone that they will not have pedals with some DC offset at the output.

The shunt cap C10 is a small 39pf. Its purpose is to prevent RF from entering the amp - the old my amp picks up radio stations condition. 39pf oight not the roll off highs you care about much, but if so, then replace it with a 22 or an 18. I like the protection. I can test this stuff too, since there is an AM transmitter a half mile away. This is a high RF environment here.

Hmmm......i'm pretty sure i removed that, tho it's been a long while. But if i recall i just have a 1 meg ground reference and a series resistor. But in any case i've never had any problems with pedals or radio interference. In fact, as stock it didn't take pedals well at all but does now. Not sure why because i trust what you say Enzo, but i'll leave it for now. If i ever have a problem with radio interference tho at least i'll know the answer.

[Enzo]

Preventive measures like those are like seatbelts in your car - until the need arises, they sit there in the way. DOn't worry about it, I was just pointing out the reason they are there.

[ahamay79]

Daz,

What's the address to Steve's site? I'd like to do that cathode bias mod.

Thanks,

Dave

Originally Posted by daz

The first mod i'll mention because i felt it was a huge improvment was to cathode bias the amp. It's actually a very simple mod. there's a gif schematic on steves site that shows the changes, but enzo recommends one difference that i found to be better......a 100 ohm cathode resistor instead of the recommended 60 ohm. This mod really opens the amps tone up and makes it transparent and much more pure and organic like a simple tube amp. the next was the C4 swap as mentioned. The mods recommend a 680 or 820 PF cap, and i found the 620 worked much better. It helps the lead channel a lot and drops the gain down a bit. the processed nasally sound is gone. The last was the input where i simplified it to a classic fender or marshall input. theres loads of garbage there that i think caused the amp to not take pedals very well.

[daz]

Wow.......this is almost a year old post ! Would have never seen it if i didn't get email notifications when someone posts in a thread i posted in !

http://blueguitar.org/

You may have to spend a lot of time looking for it because he has a ton of small text files and such and i recall the CB notes were buried in the site. Look to the "ftp" link.

[joey]

Hi. I had a Peavey Classic 30 about 15 years ago and I loved it. Having been through a slew of different Fender and Mesa amps since then, I have just manage to get an old (1994), tweed C30 on eBay in pretty good condition.

Recently, I have been modding a Epi Valve Junior and decided to do a scratch build using tag strips and 'best' components, so I have got a little amp that I consider to be the best sounding amp I've ever owned - unfortunately, it is not powerful enough to play with at gigs without sounding 'stressed'. I have tried lining it out into the C30 via its FX return, which is okay but I would like to tweak the C30 to get more 'sparkle' on its own. It sounds dull in comparison to my SE 5 watter.

I like a clean(ish) sound so I'm not really interested in the drive channel. I do play blues but it is of the vintage electric variety - T-Bone Walker, Jimmy Reed, Muddy Waters so I'm after the bright sound old old Fender amps with just a hint of grit.

I have found Steve Ahola's mods at blueguitar.com and I'm going to do the input and tone stack mods and change most of the caps to Orange Drop or micas. I have changed the EL84s to JJs and the 12AX7s to Electro Harmonics. I have a new Celestion V60 in there.

Question is, what is the best mod to add 'sparkle' to the C30's clean channel - cleaner highs, more transparency, slightly more scooped mids?

[tubeswell]

Hi Joey

I have a C30 I've modded ad-infinitum. Steve Ahola's mod to the tonestack and boost does the most for this amp (But it does alter gain - I put a 120K at the Plate of V3A to compensate). I also did the 'fenderising input' mod but with a sheilded cable from input jack to Grid pin of V1A - I used the 68k grid stopper here. I also put a 22pF RF bleed cap to ground at the input jack

I also replaced all the plate resistors in the pre-amp with metal film.

I upped the B+ and B++ by lowering R59 and R60. I have tried various combinations in here and at present have both at 8K2. This adds a certain vintagey tone to the clean channel without changing the PI too much. I have a modified Plessey/Celestion Bulldog in the amp at present. It gives the best sound yet.

In the OD channel I didn't like the stock OD sound, but I haven't quite cracked it yet. I dumped C7 altogether and made R9 into a 1M grid load resistor. I also dumped R13 and C16

I kept the 1k5/22uF cathode combo at V1A and V1B, and at present have the Rk at V2B at either 2k2 or 4k7 (I think?) with a switchable 10uF cathode bypass cap (which sounds too bassy). I have the cathode combination at V2A at 1k5 (or 1k - can't remember which) and 1uF. I don't like this OD setup much as its only any good on the bridge pickup, so I'm still comtemplating the OD channel. At the suggestion of Amp Kat I tried the SLO100 values at one stage, and the OD sounded pretty darn good with that, but lacked the fenderyness in the clean channel, which I got upset about, so I undid it. I still am contemplating revisiting the SLO100 values solely in V2A and V2B (solely because I really liked the result in the O/D channel) but with a switchable cathode bypass cap in V1A to keep the 1k5/22uF if I want it.

I did the 'proper' presence (see schematic) and MV mods, and did a resonance mod by changing R56 for a 500kA pot. These give quite a bit of flexibility to the tone manipulation. I liked these so much that I eventually hacked the amp around quite a bit to fit all the knobs and switches on the back where they can easily be got to (see photo). As I prefer the controls where I can reach them relatively easily, and as it is my favourite gigging amp of all time and I never want to part with it, I don't care about what others think - they'll never get an opportunity to buy it. :-)

[joey]

Thank you for the details tubeswell. Much appreciated.

I'm not too concerned about the OD channel. I don't understand your SLO100 reference. Are you referring to the 150K cathode resistors. These are usually 100K in Fenders, are they not?

From my experience, R19 is a critical component to the voicing of any amp with a TMB tone stack. I have a three-way switch there on my VJr giving 100K, 68K, 47K which gives various degrees of treble and bass separation. I might try that here too.

I am a bit loathe to add extra pots but I can squeeze in a couple of 3-way miniature toggles. Would tinkering with the 'presence' resistor values give me the sparkle that I'm after or is it all those small caps going from signal path to ground that is creating the wet blanket effect?

[tubeswell]

Originally Posted by joey

Thank you for the details tubeswell. Much appreciated.

I'm not too concerned about the OD channel. I don't understand your SLO100 reference.

I was talking about adopting all the resistor and cap values that are in the Soldano SLO100 O/D channel for the C30 O/D channel. The SLO100 preamp has a topology that is similar to the C30 preamp. The middy sounding O/D channel in the SLO100 sounds quite nice to my ear. I am thinking that it would be good to try this in the C30.



Are you referring to the 150K cathode resistors. These are usually 100K in Fenders, are they not?

The Cathode resistors in Fenders are typically 1k5 (not 150k). The Plate (Anode) resistors in Fenders are 100k.



From my experience, R19 is a critical component to the voicing of any amp with a TMB tone stack. I have a three-way switch there on my VJr giving 100K, 68K, 47K which gives various degrees of treble and bass separation. I might try that here too.

Be interested in your opinion of the results



I am a bit loathe to add extra pots but I can squeeze in a couple of 3-way miniature toggles. Would tinkering with the 'presence' resistor values give me the sparkle that I'm after or is it all those small caps going from signal path to ground that is creating the wet blanket effect?

The caps in the NFB don't go directly to ground in the stock configuration, there is a 10k resistor blocking the path, so the stock combination acts as a tone control. Chucking a 10kN pot mod in at R70 allows diversion of the signal from the NFB that gets through caps C53 and C54 in the stock configuration to ground. When the pot is open in the modded configuration the 150R in the mod then stops them from being reduced in value to the point where they would only bleed high frequency from the NFB to ground. The presence mod shown on the above schematic works alot better than tinkering with the 100K resistor at R57. I have tried a pot substitute for R57 initially (as per Steve Ahola's orginal mod notes) and it doesn't do much at all (I suspect due to the fact that there are all those other caps and resistors in the NFB loop). The ultimate in 'sparkle' would simply be a switch that just opened the NFB loop (I'd say between the R57 and C36 junction). I didn't want to do this because I wanted to keep the resonance mod working. Hence I went to some lengths to alter the cab to enable the chassis to be situated forward of the stock position by 22 or so mm. This gives more protection to the knobs and switches I have added on the back. Peavey should build all their classics like this in any event, to make it easier for guys like me to mod their amps. ;-)

Cheers

[joey]

The Cathode resistors in Fenders are typically 1k5 (not 150k). The Plate (Anode) resistors in Fenders are 100k.

Sorry, I'm getting cathode and anode muxed ip as usual What would be the effect of changing the 150Ks to 100K?

>From my experience, R19 is a critical component to the voicing of any amp with a TMB tone stack.

The Ahola mod changes this to 56k

I see that, but a typical Fender (or most other) TMB tone stacks would have .047µF at C14 and 100K at R19. Problem is that the C30 isn't as easy to work with as a tag strip build so I want the options hooked to switches.

The caps in the NFB don't go directly to ground in the stock configuration, there is a 10k resistor blocking the path, so the stock combination acts as a tone control. Chucking a 10kN pot mod in at R70 allows diversion of the signal from the NFB that gets through caps C53 and C54 in the stock configuration to ground. When the pot is open in the modded configuration the 150R in the mod then stops them from being reduced in value to the point where they would only bleed high frequency from the NFB to ground. The presence mod shown on the above schematic works alot better than tinkering with the 100K resistor at R57. I have tried a pot substitute for R57 initially (as per Steve Ahola's orginal mod notes) and it doesn't do much at all (I suspect due to the fact that there are all those other caps and resistors in the NFB loop). The ultimate in 'sparkle' would simply be a switch that just opened the NFB loop (I'd say between the R57 and C36 junction). I didn't want to do this because I wanted to keep the resonance mod working.

Is the tone brighter with the 10K(R70) in play or when it is shorted across? From what what I understand, C53/C54 are shunting treble to ground thus feeding back a treble cut signal that would boost mids and lows???

... I went to some lengths to alter the cab to enable the chassis to be situated forward of the stock position by 22 or so mm. This gives more protection to the knobs and switches I have added on the back. Peavey should build all their classics like this in any event, to make it easier for guys like me to mod their amps. ;-)

I noticed that in your photo. I would be inclined to have the knobs pointing downwards so that that isn't necessary but I see that you have added a speaker jack? in that position. My plan is to replace the stock speaker jack socket and pedal socket with better quality units. The stock speaker jack seems to be flaky in my amp. As I'm putting in an 8 Ohm speaker instead of a 16, I am going to wire the external jack for series to connect a 8 Ohm external speaker in series and hook up the internal speaker to the 8 Ohm tap. I'm not quite clear what Steve Ahola is suggesting in his notes but when I connect an internal 8 Ohm speaker to the stock external socket, the connection is poor and sometimes cuts out completely.

Anyway, putting extra knobs and switches in would only be a temporary stop-gap situation so that I can make variations without continually taking the PCB out and in. When I get the tone I want, I will let them be.

Isn't it amazing that we can have this dialog from opposite corners of the World

[tubeswell]

The amp is more lively (i.e. brighter) when the 10kN is open.

The effect of changing a 150k plate resistor to 100k is to incease the plate voltage, which decreases the gain/cleans up the signal from that gain stage.

I wired the internal speaker to a 1/4" socket so I could either run 1 x 16 Ohm or 2 x 16 Ohm or 1 x 8 Ohm speaker configurations from the amp. either as a combo or a head.

I too had problems with the extn speaker socket as it eventually wore out with time, and the plugs wouldn't make proper contact with the ground terminal in the socket. So I simply replaced the socket with a locally available switching socket and wired it to the same configuration as stock.

In the stock setup, the 16 Ohm tap runs through the 8 Ohm socket via a socket tip switch when the 8 ohm socket is unplugged. When you insert a plug into the 8 ohm socket, it disconnects the 16 Ohm tap and connects the 8 Ohm tap, putting both the 'internal' speaker and the extn speaker in parallel. With the Ahola internal speaker socket mod, you can simply disconnect the 16 Ohm internal speaker and run an 8 Ohm speaker/cab only from the 8 Ohm socket this way.

[Paleo Pete]

Had to let you guys know, I just got together with a local musician, working on some recording (he has a studio in town), doing guitar lessons and repairs, maybe minor amp repairs but definitely nothing heavy duty, and he has a Classic 30. First time I hooked up my Super Reverb he listened for about 30 seconds and asked why he couldn't get that kind of bass out of his C 30. It had almost no bass at all, which is why I passed up a chance to buy one for $150 several years ago. Now I'm kicking myself, I didn't know then you could modify them at all...

I got online and looked up what the knowledgeable folks here had to say, found this thread pretty quick, since it had just popped back up on the first page, and printed out the pdf file from BG.

Changed out just the bass cap, it wasn't hard to find at all but wasn't easy to get to, since i wanted to bend the board as little as possible. (it's a 30 minute drive to the nearest place to get the caps I don't have, won't be able to get over there till next week at the earliest).

Put in the orange drop, .047 I think it was, or .47 I don't have the printout in front of me as a reference, but anyway that's the only one I had so I soldered it in, put everything back together and turned it on for a sound check about two minutes before the owner came back from running errands...he walked in and I was playing my Squier strat through his C 30, soon as he looked to see what I was plugged into since my amp wasn't there, it stopped him in his tracks and his jaw fell halfway to his knees.

EDIT: It's a .047, just realized I have the PDF file on this computer...CRS strikes again...

He talked about it all day, needless to say he was very pleased with just the swap of the one bass cap, it's literally a different amp now. Night and day. I'm not sure if I'll swap the other caps in the tone section, we'll have to listen to it a few times and see how it goes. This might be the only change made, it really does sound great, he loves it. I'm not into seriously modding anything to begin with and he just wanted more bass, so this might be the only change made.

So I had to get back on here and tell you folks thanks a bunch, it was way cool to see the look on his face when he realized that was HIS amp he was hearing. (I didn't pull this as a surprise, we had discussed doing the mod, he just didn't know I was doing it yesterday while he was out of the shop).

You guys are great, thanks very much for the knowledge you share and the time you donate to doing it. He LOVES the amp now. Can't stop talking about it, plugs in and plays it any time he has an excuse to...or just wants to show it off when someone comes in and starts talking amps.

Thanks. He's a happy camper.

[joey]

Pete, can I ask which cap you replaced? The mid and bass caps are both .022µF in the stock C30 and in the mods I have seen. I have also read somewhere that for more bass it is the mid cap C19 that should be increased NOT C18 which is attached to the bass control.

In any other amp, I would just hook another .022µF in parallel with the stock caps with crocodile leads but I really wouldn't want to run a C30 out on the table!

[Paleo Pete]

Sorry, missed your question and it took a couple of days before I spotted it.

I changed C 18, bass cap. Going to probably do the mid and treble later, but have to wait until I have a chance (and a good reason, with gas over $3) to go to the larger town where I can get the 270pf cap I need.

It sounds great right now, but still not as warm as my Super Reverb, but just the bass cap made a huge difference. He still shows it off any time a guitar player comes in the store.

[tubeswell]

Originally Posted by Paleo Pete

Going to probably do the mid and treble later, but have to wait until I have a chance (and a good reason, with gas over $3) to go to the larger town where I can get the 270pf cap I need.

FWIW I used a 330pF as the treble cap and a 390pF as the boost cap (I found mica caps sounded better to my ear - other guys swear they make no diff.). When the boost is engaged, this makes 720pF for the treb cap/boost combo - less of a mid boost, more of a bright boost, and definitely more useable. I found the stock boost too harsh.

Another thing I liked was an Alnico Bulldawg - uprated to 35W RMS with a new celestion cone - gives lovely tingley highs and excellent bass, with a hint of ever sooo-slightly papery/woody quality and a nice quack to my strat. A recone is alot more individual sounding - (you never quite know what you're going to get) and cheaper too (Mine was $160NZ all up). I just used it at a gig tonight - rocks the house (unmiked).

[Paleo Pete]

Cool, thanks for the info. I've been planning to use the recommended 270pf treble cap, (mica) but haven't gotten as far as thinking much about the boost yet, and until I can get the gain pots cleaned up enough to make it usable I won't really know, but from the little I've heard while it was working some the boost sounds fairly decent so far stock. I hate to have to pull the chassis again to clean two pots, but unfortunately I hadn't tried it yet and didn't know they were really dirty until after I swapped the bass cap and put it back together. So far spraying contact cleaner down the stem hasn't done a lot of good, but has cleaned them up a little.

I'm sure I'll have to bite the bullet and open it up again, but hoping to put it off until I have a chance to go get the treble cap (30 minute drive so I need more reason than a $1.50 cap) and do that at the same time.

[Pedro Vecino]

I use 22n/22n orange drop in tone stack with 270pf polystyrene in treble and 56K slope. But boost mode is more complex: 345pF polyester Philips paralleled to 270pf and using the second circuit: 68K paralleled to 56K slope (30K aprox.).
With this system the apparent loss in bass produced by the emphasis in middle frequency is avoided and the whole tone bumps.
Regards

[daz]

I've done a lot of mods to it, tho not for gain. You can always change cathode caps and resistors to get some more, tho at the moment i can't recall what the values already are. One thing to note id the way the circuit boards are constructed it's a major operation just to swap one component unless it happens to be on the center board and you don't mind doing a snip and solder thing. You'll see what i mean when you open it. It's a real pain. The 3 boards are connected with about 100 solid core wire jupmper that get bent every time you remove the boards to do anything, and it only takes a time or 2 to weaken them to where they will eventually fracture. the tend to fracture fully right at the worse moment like when you set your amp up at a gig ! It's happened twice to me. So i'm just warning you. I paralleled every one of them on mine with bits of stranded wire so if they break again i'll be ok.

as to mods, i'd say definatly redo the input like a fender or marshall. remove all the junk there and just leave the basic components....a 1 meg ground reference resistor and a 68k grid stopper. Then definatly replace the coupling cap, i believe C7 which is a 470pf with a 680 pf or even a big larger. theres a lot more you can do, but that cap will make the lead channel less buzzy and just better sounding, and the input mods will help the amp sound more organic a bit. Go to blueguitar.org. there are a ton of classic 3o mods there. I cathode biased mine along with the mods i mentioned and it made the amp breath better and sound more natural. I also added a put where the useless boost button was which adds the boost function in to whatever extent you wish. works good for getting just the right amount instead of that horrid huge mid boost.

[kmvincent]

Thanks for the advice. The amount of info is a bit daunting for a beginner. I will check out the blueguitar.org. Maybe I will come back with some better more specific questions! Alright thanks again!

[nooneknows]

Originally Posted by daz

The first mod i'll mention because i felt it was a huge improvment was to cathode bias the amp. It's actually a very simple mod. there's a gif schematic on steves site that shows the changes, but enzo recommends one difference that i found to be better......a 100 ohm cathode resistor instead of the recommended 60 ohm. This mod really opens the amps tone up and makes it transparent and much more pure and organic like a simple tube amp.

Excuse my ignorance,
I posted in another thread about it too, I'm a bit confused.
Isn't the stock Classic 30 cathode biased? if not what the mod is about?
I'm not able to find the docs, I've found something about a variable bias via trimmer in the c30 mod on Steve's site and similiar thing for the Classic 50, but I don't remember anything about a 60 (or 100) ohm resistor (just a 10K trimmer and a %w 1 ohm 1% R, right?)
thank you in advance for your help.

[Enzo]

No, the C30 is not cathode biased.

10k trimmers would be in a bias supply circuit - for making fixed bias adjustable. the 60/100 ohm thing is referring to the cathode resistors we ADDED to make the amp carhode biased.

The mod is about modifying the amp from its original fixed bias circuit (which was also not adjustable as stock) to cathode bias. Making the fixed bias adjustable is a separate thing. In my version we made it switchable so both modes were available. I also made th fixed bias adjustable as part of the mods.

[nooneknows]

Thank you Enzo,
still I wasn't able to find the instructions to convert it to cathode bias nor on BG site (lot of 404, btw), nor elsewhere in this forum or the net, the instructions generally refers to fender amps.
Looking at the C30 circuit the cathodes are all connected to ground: I think what you've done is cutting this connction and putting a 60 ohm res in between, I imagine there should be a bypass cap too according to this page I've found:

http://people.cornell.edu/pages/mt24...hode_bias.html

is that all? (mmmh, not that easy as it seems considering the pcb of the amp..)
Please, have you a direct link to the instructions? I'm really interested in.
thank you


edited: sorry, I've found the link! I don't know why I didn't see it before, thank you!
ciao