Updates on the Classic 30 mods?

[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]

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

[nooneknows]

(ehm... it's still me...)

ok, the mods are now clear, I've found a jpg with the notes on, I'd just like to know the voltage of the 100 uF cap, is 50V enough using a 60/100 ohm R? (I don't know what is the bias current now).
Is there any problem I could be aware of doing this mod?
thank you

[Enzo]

I think we even added a 1 ohm current sensing resistor in that project.

I doubt the voltage at the cathodes of hte power tyubes will ever clear 50v, so 50v ought to be fine. I usually use 100v caps there since I have a ton of them.

You know Ohm's Law? How much current would be flowing through that 100 ohm resistor if there were 50 volts across it?

[nooneknows]

0.5 A, while I am expecting some like 100/120 mA or so, 12 V circa on 100 ohm R, right?
sometimes I forget the most obvious things....
thank you so much

[Craving4Tone]

FAO Daz

Hello Daz, I was most interested in your comments on the C30 mods (your post on January 28th you talk about the cathode bias mod), as we seem to have the same ideas of how a valve amp should sound. I have one of these amps and have found a tech who is will to help me get some tonal satisfaction. Please could you itemise the exact mods you did? Many thanks in anticipation.