I'm rebuilding my DIY Tweed to Deluxe (without the reverb and vibrato), but can't figure out what does the "C" means in the splitter on the schematic. The is also "A" on the second stage that I don't understand, I would have thought there would be a resistor to ground so this confuses me. Thanks for any advice.
If you are building it without the reverb & vibrato then "A" being the cathode bias should have the standard cathode bias capacitor and resistor of a ( standard )7025 which in Europe is a 12AX7/ECC83 .
But and this is a big but IF you want the best in this position install a 7025-WA which is an American SQ tube specially designed for guitar amplifiers -
Vacuum Tube - 7025-WA, Tube Amp Doctor, High-Grade, Premium Selected | Antique Electronic Supply
As advised by Yvesm "C" goes between the 2 -10K resistors after the Choke.
But and this is a big but IF you want the best in this position install a 7025-WA which is an American SQ tube specially designed for guitar amplifiers -
Vacuum Tube - 7025-WA, Tube Amp Doctor, High-Grade, Premium Selected | Antique Electronic Supply
As advised by Yvesm "C" goes between the 2 -10K resistors after the Choke.
The Power Magnets are out again, attracting Guitar Amplifier questions
From: the Instruments & Amps threads
To: the Tubes / Valve threads.
Welcome to the Tubes / Valve threads.
From: the Instruments & Amps threads
To: the Tubes / Valve threads.
Welcome to the Tubes / Valve threads.
Moved to the I & A forum per forum policy. Lots of knowledgeable folks here who can help answer your questions.kevinkr,
Thank You very much!
The persons who are interested in Guitar Amps will benefit (especially those who only read the Instruments & Amps threads).
Thank You very much!
The persons who are interested in Guitar Amps will benefit (especially those who only read the Instruments & Amps threads).
That's what I expected there to be, a cathode bias but the A confused me because I've not noticed that it's a repeat of the vibrato section bias.
The only difference I plan to change on this schematic is to use cathode bias on the 6V6s instead of the fixed bias. I prefer the spongier more open sound. Besides I only have 300V transformer so I expect about 6 Watts out of the amp but it's only for recording so no need for loud volumes.
Actually 6V6 ( nearly all my late 30,s up to late 40,s radios I repaired had a 6V6 tube in them I know it very well and liked it ) if its a 300V-300V transformer with anything near 100ma running the 6V6,s at 285VDC then in class AB you should get up to 14W rms at 3.5 % distortion (without NF ).
The trafo is 210V-210V. Rectified and filtered it comes up to 300V. Trafo is originally from custom Hifi amp, it used to power 4x 6GW8 so it should have enough power to spare for heavier biasing. I used this trafo in 6V6 hifi amp, it hardly got warm. Yes 6V6 is very nice tube, very warm. I build everything using them. I'll see how this build will go, and don't actually want it loud, just good sounding.
Are you sure you will get 300 V out of 210-0-210 V ? With a GZ34 you more likely get 250 V at about 100 mA.
[QUOTEyou should get up to 14W rms at 3.5 % distortion (without NF ).[/QUOTE]
I've finished bench version and think it's about the 14W, as loud as my Fender Pro Junior. I'll calculate it later. Way louder than I need. I've somewhat married the 65' and Tweed together, I'm thinking maybe I'l just make it a power amp only since I've all ready build stand alone Deluxe tube tone stack preamp. I've tried them together and it was fine.
One thing I still don't understand is why the 12AT7 splitter needs cathode resistor. I had to omit the 22k and put 68k on the cathode to ground otherwise it would work. Maybe because I've skipped the fixed bias part and just used Cathode bias on the 6V6s like the Tweed.
I've finished bench version and think it's about the 14W, as loud as my Fender Pro Junior. I'll calculate it later. Way louder than I need. I've somewhat married the 65' and Tweed together, I'm thinking maybe I'l just make it a power amp only since I've all ready build stand alone Deluxe tube tone stack preamp. I've tried them together and it was fine.
One thing I still don't understand is why the 12AT7 splitter needs cathode resistor. I had to omit the 22k and put 68k on the cathode to ground otherwise it would work. Maybe because I've skipped the fixed bias part and just used Cathode bias on the 6V6s like the Tweed.
I'm using SS rectifier and choke to get the 300V. I think I want more punch and clarity in this amp. In fact I've decided to leave my old amp alone and just build a head which will be more handy for speaker swaps. Well that's my new plan right now but that might change, it's still only a bench project now.
I've reverted the splitter and 6V6 bias back to Tweed style, it works better that way and at least it's complete as it should be.