"Post tweak" schematics

[George Adzich]

It would be nice to have some updated schematics from recent successful builds - like Dogears, Normster, Bob-I, etc.

There have been several layouts posted over the past couple of days and the authors have noted that the values are "wrong". It would be useful for many of us to see some recent "post tweak" schematics if some of you guys have time to post them.

It seems that starting with the Hybrid A Schematic and then tweaking is the general advice from most builders. But. it looks as though there are some "common" changes that are coming up over and over.

I do not find as much time to tweak these days with a newborn at home and I was hoping to use some of the wisdom of others. I have taken notes from many of the postings, but some updated schematics showing the "tweaks" would be awesome.


Thanks to all - this is an excellent forum,

George

[pedro]

heres one with some tweaked values to start you off.

cheers
Pete

[George Adzich]

Thanks Pete,

I have seen this schematic before. I was hoping that some of the guys that have posted some excellent layouts would post some of their schematics as well - Strong HINT for DOGEARS if he is checking.

He seems to have a lot of good insight and experience.


On a separate note.........................

It is good to know that I am not the only one that pisses off the wife by staying up late in the garage working on amps.


-George

[pedro]

George,
there are some subtle changes on this schem which reflect some of the best advice Ive received.
Its not the same as the original schem which you will have seen - I amended the values of critical components. Dogears had a large part to play !

cheers
Pete

[tonelab2]

What format is .ppt?
Can't open it without the right program.

[pullshocks]

You can download (free) Power Point Viewer from the microsoft.com web site.

[Bob-I]

Mine's already posted in the files section.

[tonelab2]

Thanks Bob.

[George Adzich]

Thanks Pete and Bob!

Bob,

I thought that you had made some changes to your circuit since posting the "3 channel" schematic.

I was planning to use your schematic as my primary starting point and tweak from there. I just thought it would be a good idea to see what "tweaks" the other members came up with.


-George

[dobbhill]

For those without PPS....
D

[dogears]

There are a few problems with this schematic.

1) PAB switch is a dpdt and MUST break the bass pot wiper as well.

2) CL2 grid bypass cap is a 500pf and not 470pf

3) If the amp is a dedicated HRM build, I woudl use the .0022 OD1 cap and 250ka gain pot just like the schematic calls for.

4) Disregard the voltage measurements. Shoot for 200v on V1 and 210 on V2. If you must, adjust the string closer to Hybrid A. Also, you need to hang a 150k to ground to simulate the FET. (off of the last resistor) Please erase these measurements from the PDF as they are pointless.

5) 270pf bright cap is too big IMO. Try 120pf

6) 47pf bright cap on clean master is too big for my tastes. Try something around 22pf. Experiment.....

7) V1B cathode resistor is a 2.2k Typo in PDF

8 ) Experiment with V2a cathode resistor. I think I have a 2.94k in mine against the 182k RN65 plate.

9) Experiment with the V2B grid resistor. With the 100k drive pot in this PDF, I think a 180k would be more appropriate. 150k won't be as smooth as 180k. Depends on amp brightness. I run a 180k.

10) My PI input cap is a .022 I like it more than .01 I run 6L6 tubes.

11) I run 100k and 110k for PI plates with a 20k trimmer. Shoot for about 110/120 including trimmer size

12) I use 270k as the main cap balance resistor. Never saw 330k.

13) Measure all parts. Make sure pots are fully valued.

Adjust HRM with PAB boost on ONLY.

Maybe someone wants to make these changes??

For those without PPS....
D

[jaysg]

Is there a best version non-HRM schematic here somewhere? It looks like Norm's layout is non-HRM but has reverb -- couldn't find a schematic for it.

[dogears]

The Hybrid A is close. If you want, I could detail my changes to you.....

Similar stuff to the above list. Disregard voltages, 500pf bypass cap, 150k over OD level and NOT a 330k, use Skyline stack w/midcap switch between .047 and .01, etc....

Is there a best version non-HRM schematic here somewhere? It looks like Norm's layout is non-HRM but has reverb -- couldn't find a schematic for it.

[jaysg]

That's okay. I should probably draw mine up as clearly as I can and post it for comments...one more thing on the list...

[dobbhill]

Sorry about the incorrect values on the PDF. I have a PDF conversion utility but not real editing software. I'll try to figure a way around and make those vital changes ASAP and re-post. I doubt that many have spent near the tweaking time you have, Dogears, but those voltage measurements came from ODS #200+a few and I've always thought they were a good starting reference. Of course, we've had recent discussions here about the type, quality, and vintage of tube that goes "in the hole" so......here we are.
Also, thanks for sharing your backing tracks - wonderful collection!!!!
D