<![CDATA[Music Electronics Forum - Mods & Tweeks]]> http://music-electronics-forum.com/ en Fri, 20 Nov 2009 21:44:05 GMT vBulletin 60 http://music-electronics-forum.com/images/misc/black/rss.jpg <![CDATA[Music Electronics Forum - Mods & Tweeks]]> http://music-electronics-forum.com/ Need someone more knowledgeable http://music-electronics-forum.com/t16227/ Fri, 20 Nov 2009 19:03:40 GMT Looking for someone with a little more experience to advise me regarding a current build. It's a basic 5F1 - repl. Fender trannies, tube recto, etc. Changes I've made are 1) beefed up supply caps: 40mfd/500v, 20mfd/500v, 20mfd/500v, 2) lower supply resistors for a little higher voltages 1K/1W, 10K/1W, 3) addition of 1N4007 diodes to recto inputs/outputs (ss bridge backup for 5Y3), 4) ability to switch in simple tone stack (5E2 tone control), 5) switchable RC cathode circuit at 1st gain stage (25mfd/1.5K, .68mfd/2.7K) 6) switchable NFB level which all should work with no problems I'm aware of other than 40mfd 1st supply cap is maximum a 5Y3 can handle. Regarding this I've 2 relatively simple questions. I know I can experiment & find this out on my own but... soooo... my questions...

1) since I'm using all new top quality components I no 2.7K resistors in my box & don't wanna wait 3 or 4 days on the UPS driver... Would it change things much if I substituted a 3.3K resistor or if it's thought better a 1K & 1.5K in series?

2) The stock NFB resistor value is 22K & I know omitting it increases gain but not always desireable so I was thinking of adding a switch that instead of eliminating entirely would drop a lower value. 2 ways I've considered doing this are switching in a 2nd 22K resistor essentially cutting the resistance value by half if I remember my training from electronics school so many moons ago or just switch the stock 22K out of the circuit switching in a lesser value... thinking 1/4 or 5.6K value. Can anybody suggest which would be the way to go??? Keeping in my I'm looking for a modest but noticeable increase in gain. Also is would there be any benefit to also adding a cap to ground HPF in the NFB loop? If so any suggestions as to what value might work well .01mfd, .1mfd, larger?

Any help would be much appreciated... pix of this build to follow shortly. ]]> http://music-electronics-forum.com/t16227/ Mesa GEQ - Changing the freqency. http://music-electronics-forum.com/t16224/ Fri, 20 Nov 2009 17:55:27 GMT I have a Mesa DC3 and the GEQ jumps from 2.2k all the way to 6.6k in terms of frequency control. I find 6.6k to be too high to be useful for guitar;... I have a Mesa DC3 and the GEQ jumps from 2.2k all the way to 6.6k in terms of frequency control. I find 6.6k to be too high to be useful for guitar; most guitar speakers roll off severely after 5k. I'd be happier with that control in the 4.5 to 5k range I think.

Mesa uses a .033uf cap in series with a .033H inductor to get the 6k value; what should I use to get 5K ish? Can someone hip me to the correct formula to calculate the frequency I want?

Also, any suggestion on a source for the inductors?

Thanks! ]]> wizard333 http://music-electronics-forum.com/t16224/ Crate V1512 mods http://music-electronics-forum.com/t16200/ Thu, 19 Nov 2009 02:58:42 GMT I've been checking out several sites for mods that will make a difference on my V1512. It has the celestion 70/80 speaker ( I've got a G12H-30, but it stays with my stealth GT50H... always). I've already cut the cap at C38 and it decreased the gain a little, but didn't round out the sound like I had hoped. Don't get me wrong, I LOVE high gain, but the V's a little fuzzy compared to my stealth although they complement each other well when AB'ed. I like a hard driven Zakk Wyldish sound that's crunchy and full of harmonics at the same time. And the boost button is too dark and mushy to be of any use to me. Has anyone tried a new OT? Can anyone give me a list of mods for the V1512 that could take out the fuzz and bring on the pain, yet still clean up a little by turning down the guitar volume? Any ideas will be considered and appreciated. ]]> David Ray http://music-electronics-forum.com/t16200/ Is this amp PCB layout familiar? http://music-electronics-forum.com/t16198/ Thu, 19 Nov 2009 02:10:33 GMT I believe this is the PCB for the PV Ryl 8. I do have the parts spec listing - was unsure if it woiuld help? 1. I wonder if any of you experts... I believe this is the PCB for the PV Ryl 8. I do have the parts spec listing - was unsure if it woiuld help?


1. I wonder if any of you experts recognise this layout?
2. If the layourt is a historically conventional one?
3. I wonder what they based it on and if there are any optional Mods - - and how the mods might sound.

Thank you all in advance

PS CABLES:
At the guitar store a fellow compared similiar genereic cables vs Monster cable dnd the generics seemed quite dull and most definately "quieter"/ less eifficient compared to Monster but I think monster are a ripoff and too blingy and the plugs apparently are not well designed and bad for standard recepticles. This simple cable comparison in a small amp sounded like a speaker upgrade with a couple addnl db's sensitivity - I was astonished.

I have been using generic cables and am ordering some Canare gs-6 with Nutrik Silent Plugs for it.
Attached Images
File Type: jpg PCB outline.JPG (66.9 KB)
Attached Files
File Type: pdf ValveKing_Royal 8 SCHEM.pdf (22.5 KB)
]]> CSPRINGER http://music-electronics-forum.com/t16198/ 5E3 Half Power switch http://music-electronics-forum.com/t16156/ Mon, 16 Nov 2009 15:25:21 GMT Hi there, I tried this mod suggested in the 5E3 Forum, it seems to really work as a bright switch, or a dim switch to be exact. I loose grind to... Hi there, I tried this mod suggested in the 5E3 Forum, it seems to really work as a bright switch, or a dim switch to be exact.

I loose grind to be exact, I love the tone of the 5E3, and this mod supposedly is an attenuator.

As far as my setup here, I've got 510R 5W cathode resistors, 22uf 25V bypass caps, and the resistors on the switch are 330R 1/2W, and 100K 1/2W.

Is it a case that the 330R and 100K should be higher wattage to attenuate more?

Thanks in advance,

Leif
Attached Images
File Type: gif da_Geezer.gif (4.1 KB)
]]> Leif H http://music-electronics-forum.com/t16156/ Hola! Perhaps you awesome peeps can resolve my query on bias.. http://music-electronics-forum.com/t16126/ Sat, 14 Nov 2009 19:30:14 GMT I own a Splawn Quickrod. Voiced pretty well, but I'd like to try either KT66 or 6L6 tubes instead of EL34. I've been told I'll have to perform a bias mod in order to accomplish this change.

Now, I understand completely that Capacitors can store lethal voltages. Good thing I can drain them. So if I die attempting to follow your advice, you're off the hook now, and it is entirely my own fault when I find myself in a dark tunnel gazing at a bright light at the end of it.

I'm basically just trying to prepare for a mod if I can't set my bias low enough to accomodate a 6L6 pair. ]]> korovamilkdud http://music-electronics-forum.com/t16126/ Crate Stealth GT50H Mods http://music-electronics-forum.com/t16115/ Sat, 14 Nov 2009 01:28:29 GMT I was looking at some of the suggestions on an earlier thread about the voicing of the Crate Stealth GT50. It is a one trick pony as far the lead... I was looking at some of the suggestions on an earlier thread about the voicing of the Crate Stealth GT50. It is a one trick pony as far the lead and crunch channels are concerned. I was wondering if I added a choke to replace R89. The schematic was on the earlier thread, but it's the first 5 Watt 470ohm resistor after section A in the power supply. I believe this is the normal placement for a choke. I was wondering if it would smooth out the raspiness and give a little more vibe to the amp. Most 40 watt and above amps have chokes and I wonder why these amps don't. Any suggestions? ]]> David Ray http://music-electronics-forum.com/t16115/ Should I add a bypass cap in a cathode-biased amp? http://music-electronics-forum.com/t16077/ Wed, 11 Nov 2009 22:07:08 GMT The Silvertone 1457 amp-in-case is a small single-ended amp equipped with a 6X4, 2 x 12AX7 (one for the tremolo) and one 6V6. This amp has got a 270... The Silvertone 1457 amp-in-case is a small single-ended amp equipped with a 6X4, 2 x 12AX7 (one for the tremolo) and one 6V6.
This amp has got a 270 ohm cathode resistor on the 6V6 but NO bypass cap: the cathode resistor goes to ground with a 33 ohm resistor in series, and goes also to the cathode of the 12AX7 tremolo tube.
Should I add a bypass cap across the cathode resistor? Or does this circuit design not involve a bypass cap?
Also, this amp has got very low volume: compared to a Fender bf/sf Champ it is much less loud. The B+ is lower than the schematics (around 280V instead of 320V), and swapping the power tube did not yield any difference. The 6V6 is biased around 12-13W at idle.
The schematic is in attachment.
TIA,
Carlo
]]> slidincharlie (Carlo P) http://music-electronics-forum.com/t16077/ 1/2 power switch? http://music-electronics-forum.com/t16054/ Tue, 10 Nov 2009 20:35:37 GMT I'd like to install a 1/2 power switch on my Crate VC50. Its fixed bias with 4 EL84"s. Am I correct in assuming all Id need to do is wire a STDP switch between pin three and ground on two of the EL84'S ? (after of course cutting the trace to pin 3 on those two tubes) If so what minimum rating should the switch have? Thanks Bob ]]> rockon1 http://music-electronics-forum.com/t16054/ Gibson GA 40T Effect Loop? http://music-electronics-forum.com/t16050/ Tue, 10 Nov 2009 11:04:22 GMT Hi! I got this wonderful Gibson GA 40T Amp and love it!
But i'm a greedy man, i wan't reverb!
so i thought i would make a effect loop (between the preamp and the poweramp) to have the reverb effect after the pre amp.
But i'm just not experienced enough to read the schematics.
Can anybody guide me though this mod ? Or talk me out of it if it's not a good idea ?

Simon.
Attached Images
File Type: jpg 1962_Gibson_GA-40T.jpg (34.3 KB)
File Type: jpg GA40T.jpg (273.5 KB)
]]> shades http://music-electronics-forum.com/t16050/ EQ in the FX loops as a master volume? http://music-electronics-forum.com/t16041/ Tue, 10 Nov 2009 03:16:22 GMT I've seen a few of the aftermarket master volume knobs that plug into the effects loop on a tube amp to control the overall output.

Will using the level control on an EQ pedal inserted into the loop accomplish the same thing? ]]> glocker199 http://music-electronics-forum.com/t16041/ <![CDATA[any tube guys out there have exp with el506's?]]> http://music-electronics-forum.com/t16037/ Mon, 09 Nov 2009 23:24:54 GMT i have an old selmer amp which i've never used. i bought it a while back as a project but realised after how sparse el506 seem to be, they arent produced anymore it seems.

anyway, i was comparing the specs of el506 to el84s and they dont appear THAT far away. little bit less output/maximum voltage etc.
it would mean adjusting some voltages obviously, but would the OT be ok with less power going through?

would a conversion be worth it?

the amp is a selmer compact 30, i think it would be pretty cool as a head :) ]]> kepeb http://music-electronics-forum.com/t16037/ How to add bias adjustment to a Mesa 20/20 amp? http://music-electronics-forum.com/t16034/ Mon, 09 Nov 2009 22:38:55 GMT Looks like the fixed bias is at -14V. Anyone do this? How did it work out? Being able to optimize the bias for EL84s seems to make sense to me, but... Looks like the fixed bias is at -14V. Anyone do this? How did it work out? Being able to optimize the bias for EL84s seems to make sense to me, but maybe it's not worth the trouble? What do you think? Thanks! ]]> crazytooguy http://music-electronics-forum.com/t16034/ Rectifier diodes http://music-electronics-forum.com/t16003/ Sat, 07 Nov 2009 20:18:49 GMT Will these work in place of a 1N4007? near as I can gather they should but I just want to check with those who know better. Heres the specs ... Will these work in place of a 1N4007? near as I can gather they should but I just want to check with those who know better. Heres the specs


Temp range -85 to 320 F
peak inverse voltage-1000v
foward current -1.5A
peak surge current(8.3ms) --50 A
foward voltage drop(VF)at (lf)- 1.1V
peak reverse leakage current at(77* F)-5.0uA
typical total capacitance 20pF
typical thermal resistance junction to lead-77*F/W
typical thermal resistance junction to ambient- 131* F/W




Thanks Bob ]]> rockon1 http://music-electronics-forum.com/t16003/ <![CDATA[I want to convert 6L6's to 7591...]]> http://music-electronics-forum.com/t15995/ Sat, 07 Nov 2009 05:50:50 GMT First of all, I love the sound of this tube. I love how it stays clean all the way up and then only get's a little bit of grit to it. It's just an edge.

I have a couple of 7591 tube related questions.

1.) I have 2 amps that both run with a pair of 7591's. the problem is, that one is a 25 watt amp, and one is about a 18, or so. I just wish I could have the tone and edge of a 7591 but with more power. About 40-50 watts.

I know that with some pin layout change, that you can sub a 6l6 for a 7591. I'm wondering, can i do it the other way around, and what would it take, mod-wise? I really am set on 7591, so don't just say, stick with the 6l6...

the reasoning behind it is, fender hot rods and devilles are really plentiful around here and a good bang for the buck, and I know they both use 6l6's.

Or maybe I could take an amp that had 4 6l6's and replace them all with 7591's...

That is my first question.


2.)I have an ampeg rocket 2 that uses a 7591 pair, 1 12ax7 and 1 7199. I also have a 1965 epiphone futura that uses a 7591 pair, 2 12au7's, 4 6eu7's and an OA2 tube regulator.

The epiphone is rated at 25 watts, and the ampeg is rated at like 18-20 watts. That seems reasonable considering that they both use the same power tubes. when I crank the epiphone all the way up, It stays clean! I am talking about all the way up, volume wise! I mean, It doesn't stay totally clean, but it doesn't distort, it just gets edge. and it's smooth edge. and it's much much louder then the ampeg. taking in the difference in speaker size too...

but when I crank the ampeg, even just to 2-3 o clock, it get's really fuzzy, and distorted. and it's not as warm, either... It seems very very cold in comparison to the epiphone futura. So I'm wondering, besides the epiphone having a whole slew of pre-amp tubes for the tremolo and the reverb that comes with it, what could be the main difference between these 2 amps?

could the ampeg be biased too cold?

3.) I had purchased a set of 7591 tubes in case either of them went out on my 2 amps, and sure enough the epiphone futura was making this wierd crackling noise whenever I would strike a chord hard, and so I switched in the new set of tubes I had bought. They were sovtek 7591's that I bought on a bad impulse while in my local music store. I have since come to find out that they are actually really close or identical to 6l6's, and that they can be used, but with a bias modification...

I had heard that any new power tubes will be matched differently then the NOS ones that had been in the amp before, and I just figured that i didn't care if the tube life was shortened by a little bit, if it sounded ok then. Now I am wondering if I am messing something up by using these supposed "6l6's" They aren't running that hot, but hot enough. They look totally fine, and if I hadn't read it online, I wouldn't have noticed a thing...

considering that I love the tone of this epiphone when it has "basically 6l6's" in it, I am wondering If i'm right in my quest for 7591-ness...

well, anyways...


I know that's alot, but thanks for reading, (if you did...) and thanks in advance for the answers that I hope I will get.

-Noah. ]]> Bmxbarspin724 http://music-electronics-forum.com/t15995/