Couple of Questions on Peavey C30 Tweed Bassman mod

[tubeswell]

Talking about David Becker's notes on modding the Peavey Classic 30 with the 'Tweed Basman Mod" on the Blue Guitar website.

So here I am stuck out in the backwater of the tube amp modding part of the planet that I am, and I can't get specified parts for the mod.

"Silver Mica caps" the shop assistant said - "never heard of them". So I managed to scrounge some polyester caps of nearly the same values (well actually a few 390pf a few more 360 pf and some other oddball values, which if I put in various combinations of series and parallel I can just about approximate 680pF in step 5 and not quite the 47pF in step 17). Comparatively minor frustrations.

Anyhow, I can't get a 25uF/25wvdc electrolytic (whatever that is) for the v2A cathode bypass cap substitute in step 8, so I presume a 22uF/25V electrolytic will give me damn near the same effect - feel free to correct me if I'm off base.

What's more, in Step 21, I can't get 1W 5k resistors anywhere in town so I presume 4.7k 1W resistors will be okay here (or should I go to 5.3K? - which is 'safer' - higher or lower?)

But the bit that's really got me stumped is step 12. Please see the attached .pdf. Can anyone tell me if I've got the arrow pointing to the correct trace in question? I understand this is fairly critical.

[hasserl]

Yes, the 22uf cap will work fine for the 25uf, and the 4k7 resistors will work fine for 5K. And polyester caps will be fine in place of silver mica. The main thing is to upgrade from the ceramic discs that often get used in these small capacitance ranges.

Haven't a clue about step 12, do you have a link to the mods so I don't have to go searching The Blue Guitar site?

[tubeswell]

The Bassman mod schematic, the stock C30 schematic, and the stock C30 layout are on these links (Courtesy of Mr Ahola).

http://www.blueguitar.org/new/articl...y/c30twdbm.zip

http://www.blueguitar.org/new/schem/peavey/c30schem.gif

http://www.blueguitar.org/new/schem/peavey/c30layg1.jpg

I have attached the mod notes that make numerical sense (because the other set of mod notes confuses the step numbering a bit)

[Enzo]

I could have sworn we discussed this already.

Look at the schematic, you are going to eliminate C2 and wire across where it is in the schematic. The right end - looking at the schematic not the board - of C2 connects to a relay contact that will go to ground in one state. Wuthout C2, that would ground off the B+. We have to disconnect the relay from that circuit trace.

Forget numbering the pins on the relay, the trace to cut is the one going to C2. And that is the one your arrow points to with the highest authority.


You know how sometimes people confuse V1, V2, V3 in an amp with tube #1, tube #2, etc numbered left to right. V numbers refer to the schematic. It is convenient when they are also in the same order in the amp. But many times they are not. SO when someone says V3 is the phase splitter because it says so in the schematic and someone else says no no it is V5 because it is the fifth tube over, things get confused.

I think that happened here. One person counts the pins on the relay and numbers them 1,2,3. SOmeone else looks on the schematic and sees numbers and assumes they mean pin numbers. They don't. The numbers on the schemo are for the drawing software. Notice all the resistors have "pin numbers." The diodes and some of the caps have pin numbers. Even the pots have them. Those are not pin numbers. Look at the pot, come to think of it, the ends are "pins" 1 and 2, and the middle wiper leg is called 3. That ought to confuse someone.

Schematic software works by listing connection, so it gives each leg of a part a number so it can describe a circuit as resistor 15 pin 1 to V1A pin 3, and resistor 15 pin 2 to ground. The Capacitor 12 pin 1 to V1A pin 3, and capacitor 12 pin 2 to ground.

Further confusion is possible when a relay is laid out like an IC, and would have like 16 legs. This relay only has 8 legs, but they will often assign the numbers to the pins as if all 16 were there. Just like a 6L6 numbers the pins as if all 8 were there even when only 6 are on the tube. SO instead of pins 1,2,3,4 down the side, it might be actually pins 1,4,6,8.

[tubeswell]

Hi Enzo - we did discuss this, and as you rightly surmize the numbering did confuse the hell out of me. But now I am totally 100% confident which trace to cut. Thanks once again.

[donbenjy]

Hi, I just stumbled across this site, and thought I'd post here instead of making a new thread!

I've just done the tweed bassman mod to my classic 30, and it sounds great, although it is a little harder to drive the power amp than I expected, but I'm currently in halls, so anything past 1 is pretty much a nono

Anyway, the reason I'm posting is because I noticed the amp gets VERY hot really quickly. I've just done a test run for about 20 minutes and the chassis, particularly over the EL84s is almost untouchable. Now before the mod it did used to get that hot, but nowhere near as fast (at least from what I remember, I think it took around an hour, maybe less, to get to to that heat). I know that 2 power resistors were changed to bring up the preamp plate voltage, which I thought might have done it, but as I said, the heat seemed to be above the power valves.

It'd be awesome if anyone could offer an insight to why this is happening, and if it's likely to be dangerous? I've also noticed that it's possible to hear a small amount of sound with the volume at minimum, which I'm fairly sure wasn't possible before (though there was one time when I was messing around with oscillating pedals that did it, but that was seriously loud). You can't really hear harmonics or anything through it, but you can hear a tonal change when the pickups are switched, so there is sound (and I started out with oscillation before I plugged my Strat into an untested amp, which came through loud and clear with the volume at zero). This all might be hyperchondria to be honest, but I think it's worth mentioning.

At the minute I'm not particularly worried by these, but as this is my first amp mod then I don't want to take any chances and I want to make sure I've done it right. If the OP has actually completed the mod successfully, it'd be good to hear his experience.

Thanks guys!

DB

[Rob Mercure]

Donbenjy,

Instead of "hijacking" - as we say around here - a truly old only semirelated thread please do make a new one. It saves confusion for everyone. But only one.

Thanks, I'm sure lots of folks will be glad to look at and help you once you do.

Rob

[Enzo]

Yeah, Hi there DB, and welcome to the forum. I agree, you will get a lot more response with a new thread instead of adding onto one that has been dormant for over a year. New threads don't cost much, we get a discount.