Tube Amp Archive

Well, I made some major improvements last evening. I dropped the first resistor in the PS to 1.5K from 10K. Valves are V4 - 6L6, V1,3 - 12ax7, V2 12at7 B+ is now: A - 339 B - 328 C - 304 D - 294 V4 with 200 ohm on the cathode Plate - 319 Screen - 307 Cathode - 18.09 This should get me to about 87-88...

Hey All, Just an update. I have the amp working, and with initial listening I am baffled by a few observations. First, I have little low end authority. I'm listening through a 12" Cannabis Rex and the Low E just sounds anemic/fuzzy. Secondly, I'm distorting quickly into rotation of the vol pot. I wi...

While I'm still waiting for shielded wire for input and vol pot, I did finish wiring up the amp and have initial voltages to report. V1 A 158v 1.327v V1 B 155v 1.35v V2 272v 2.66v V3 A 163v 1.34v V3 B 163 1.416 V4 342v Plate 271v Screen 18.01 Cathode (currently 300 ohm) Id like to see a few more vol...

In pentode mode?
How long will the tube last at 90-100%

Yep, you were correct. With the filter caps and choke I'm about 416 vdc with all tubes conducting other than the output tube. I still need to wire in the switchable cathode caps and resistors for the output tubes. What is a realistic plate dissipation for both the EL34 and the 6L6? I want to bias fo...

Hello All, Probably premature, but I have a question on my build. I'm finished with the board and have most of the power circuit wired up. I've tested the output of the tube rectifier at 347Vdc. Strangely, the SS rectifier is giving me an output of 287Vdc. These voltages are taken at the base of the...

and a little more progress...

First time making a turret board. I'm happy with it!
Hardware gets mounted tonight!

Progress.... The chassis is drilled front/back and sockets. I need to cut out for the PT, and figure locations for RT, OT and choke.
The layout is complete and I'll start drilling the G10 for turrets tomorrow. Its going to be a rainy day so good times to get some more work done!

Thanks Craig,

I made that adjustment to the schematic, as I was reminded the 22K is way too high.
I'm going to play with 2-5K and see what works best in the amp.

I appreciate the "eyes" on the design.

I'm hopeful it will work when I'm finished...???

BK

Here is the most recent schematic and PSUD sim.

I've probably made a bunch of incorrect assumptions on PSUD...

Thoughts?

Hey Fellas, Hope you are all well. Would anyone care to suggest operating points for the 6CA7/EL34 and the 6L6? I'll have switchable bias resistors for 6CA7/EL34 and the 6L6, but looking at the tube data it seems they don't like to operate at similar plate voltages. The reason I ask is that I'm tryi...

Good call. I wouldn't have noticed that change in NFB value.

What do you think about the filter cap values in the PS?
I"m trying to keep the first cap low enough for the valve rectifier, but want some reservoir capacity hence the second larger value at Node A.

Thanks!

Bryan

I've updated the schematic to account for NFB at V3b, and I've added in the SS rectification option.

I'm hopeful to get the layout hand drawn in the next few days.

Does anyone see any issue with the schematic before I proceed? I think it should make sound...

Very nice!!!