Tube Amp Archive

I'm thinking of leaving the stock bias, as shown here below. Cutting the trace that goes to the Grids, making the stock bias supply V5/6. Then making another of this bias circuit on a perf board. Tying into the diode bridge and ground, and then the output going to V7/8. A trimmer for each side - tak...

I added a question/changed the title to reflect the question. Thanks for the replies so far.

I forgot to add I also already have one bias control - a resistor in series with pot - in place of R49

I have a Ampeg v4 that was converted to run 6550s. Someone put one bias resistor on Pin 8 of one of the power tube sockets. I decided to add three more to check the bias of the other 3 tubes. When I got the amp, it only have two 6550s - the guy was running it at half power - so I ordered two more. T...

Increase C29 to 22 to 25 uf. Do you mean to 22 or 25uf? With just a ratty little 12AX7 section, Boogie reverb circuits can't drive much nearly as much power into the tank as Fender reverbs that use a parallel pair of 12AT7. I'd look at trying a JJ ECC823 to push more signal into the tank (and linki...

I wanted to know if there is a way to increase the wet mix on the Reverb. I upgraded the reverb pan and that helped but even with the Reverb mix all the way up it still isn't as wet as I'd like it to be. https://reader012.staticloud.net/reader012/html5/20180615/54f9b5e34a7959d7638b5075/bg5.png https...

Thanks. Worked great!

For the adjustable bias, I was going to add cathode resistors - which given the schematic means adding the 1 ohm resistor between Pin 8 and ground, right? I need to cut the traces for Pin 8.

I’ll have to put the 47k R81 back in and read it.

I put the bias mod in as initially suggested and was only getting 18MA. That was with a 22k in series with 50k trimmer in place of R81.

I measured 480v off the plates so I was looking for bias it at 30ma or so.

Would be I putting the R81 47k back into the circuit and then adding an additional 47k with the 10k trimmer? Looks here like someone added a 10k trimmer in series with R65: https://el34world.com/Forum/index.php?topic=9385.0 https://el34world.com/Forum/index.php?action=dlattach;topic=9385.0;attach=25...

Do I need to tie the wiper to one of the outer lugs of the trimmer? I have a 22k resistor on hand and had purchased a Bourns 50k trimmer.

I picked one of these up and the clean channel is really nice. Don't care for the gain channels but given I paid $100 for the amp I'll use the clean channel with pedals. Looking at the schematic, I was thinking making R81 a trimmer would allow for adjustment of the bias? I've been unable to find any...

So I did the mods Markusv and M Flower suggested: Thanks to you both. Amp sounds pretty good. Another guy had sent me his augmented CHB-100 schematic and one of his mods was to move the Master volume to right after the 12AX7 stage and before the 6C4. I tried it and it produces lots of gain! very gra...

For my suggestion, the one half of the 6EU7at the input: Typically /traditionally there is a 100K resistor connected to the plate of the tube. Then there is a parallel 1.5K resistor/22uf capacitor between cathode and ground. It will drive the following stage a bit harder for better breakup etc Plea...

whats the purpose of both of these? Can you point to them on the schematic? I'm aware of the screen and grids for the 6l6s Your amp doesn't have either and it would be a good idea to add them. 470ohm/5w screen pin 4 on each 6L6GC tube socket where it says 420v coming from your power supply. 1k5/1w ...

I used to have 2 of these I think the biggest change I made were the jacks and changing V1A setup to 100K anode resistor and a 1.5K/22uf combination at cathode . May be due to the phase splitter in that amp - not sure- but if driven hard these amps sound glorious Markus V Could add 470R/5w screen r...