Layout updates and schematic, (about time)

[BobW]

Please critique for errors. Thanks especially to Bob-I for allowing me to use his initial VISIO drawing as a schematic baseline.

[jaysg]

The bias supply diode is backwards on the schematic and I believe you might want to reverse the positions of R6 & R7 so that the 100K, 1W is connnected to the secondary. B1 is on the wrong side of the Standby switch.

[rutledj]

I'm a noob but I don't see a link to actually view the files. What am I missing?

Thanks,
Rut

[dogears]

Bob,

Why not add the bypass cap switch on CL2. I like 10uf there. The V2 tube doesn't need the switch IMO.

Also, I like 500pf bypassing the CL2 220k grid resistor.

Go with the ubiquitous 270pf snubbers with this recipe. It will balance the lows.

Lastly, aside from Dumble using linear pots for the OD drive and level, I also can't imagine why anyone woudl want audio tapers there. Tried it and the range is all wrong.

[tictac]

Personally, I like the audio tapers for the drive and level; it's easier to dial in the amount of distortion and overall volume with audio tapered pots. I think Dumble used linear pots because that's what he had on hand. Besides once you turn them up all the way they're both the same.

[BobW]

The bias supply diode is backwards on the schematic and I believe you might want to reverse the positions of R6 & R7 so that the 100K, 1W is connnected to the secondary. B1 is on the wrong side of the Standby switch.

You are correct, I should have redrawn the Pwr/Bias section, rather than copy Bob-I's schematic, without checking. That makes his initial schematic incorrect also. Bob, you may want to recheck your schematic too? Thanks for catching the errors.

I'm a noob but I don't see a link to actually view the files. What am I missing?

You're not a noob, I simply posted a jpg of the visio file. It's too large to post.

Why not add the bypass cap switch on CL2. I like 10uf there. The V2 tube doesn't need the switch IMO.

Also, I like 500pf bypassing the CL2 220k grid resistor.

Go with the ubiquitous 270pf snubbers with this recipe. It will balance the lows.

Lastly, aside from Dumble using linear pots for the OD drive and level, I also can't imagine why anyone would want audio tapers there. Tried it and the range is all wrong.

Dog, the bypass switch is a good option, just haven't implemented yet. Will try the 500pF bypass, and 270pF snubbers. I assume you mean snubbers on both OD1 and OD2? I only had Audio pots at the time, will also try linears here after your other suggestions. As always, thanks Dog, your insight and ears know best.

Personally, I like the audio tapers for the drive and level; it's easier to dial in the amount of distortion and overall volume with audio tapered pots. I think Dumble used linear pots because that's what he had on hand. Besides once you turn them up all the way they're both the same.

I appreciate your input, but usually don't turn these pots up all the way, it sounds too muddy. The drive is about 11 to 12 o clock, and the OD level ranges from 11 to 2. Anything more on either pot is too overdriven, imo, besides, I now have linears at my bench, to give Dogears suggestions a try.

[rutledj]

for some reason when I view this thread at home in IE or Firefox, I don't see the pics. When I go to work and look I can see them.

Does anyone have a clue what causes this problem?

Rut

[George Adzich]

BobW,

Please let us now what happens when you try the Linear Pots on the "Drive" and "Level" controls

It looks like you covered most of the changes that have been suggested on the board with the addtions from Dogears in the last thread.


Cheers,

George

[BobW]

Please let us now what happens when you try the Linear Pots on the "Drive" and "Level" controls
It looks like you covered most of the changes that have been suggested on the board with the addtions from Dogears in the last thread.
Cheers,
George

Will do George, I picked up the parts yesterday, but won't get to it till the weekend. I had asked Dogears about the 270pF snubbers, and I assumed he meant at OD1 and OD2? I'm only using one at OD1?

[BobW]

Here's the latest changes I performed.

swapped 390pF to 500pF on the 220K, this made the amp more alive w/improved bottom end.

270pF snubbers at both OD1 and 2 , also an improvement.

Dogears, am I missing something here? I swapped out the OD drive and master pots to linears, and as expected didn't notice a change in tone except for the ramp rate log vs linear.

10uF at CL2 seemed a bit much w/ humbuckers, and it didn't add that much more w/single coils, so it was changed back to 4.7uF. (switch real estate area was probably the main factor for this decision)

thanks to all for your help.

My next build adventure will be either a 50 or 100W w/HRM and dumbleator.

[rutledj]

Can someone tell me how critical the values are for the PS caps? Are 40uf too large to use here?

Thanks,
Rut

[George Adzich]

BobW,

It would be great if you could update your schematic with the final changes that you called out in your last post.

Your schematic seems to be very close to the "ideal" Hybrid-A "Starting Point" that many people have asked for.

What was the final verdict on the Level and Drive pots?? What taper worked out the best for you - Linear or Audio??


-George

[BobW]

George, I plan to update the schematic soon. The only change, IMO, linears vs. audio was the gain slope change. I left the linears in.

[glasman]

Can someone tell me how critical the values are for the PS caps? Are 40uf too large to use here?

Thanks,
Rut

The general concensus is that 40uf on the Screens, V2 or V1 will make the amp overly stiff and lose some it's feel.

20 or 22uf is the better choice with 2-220uf's in series for the first filter bank.

Gary

[BobW]

The general concensus is that 40uf on the Screens, V2 or V1 will make the amp overly stiff and lose some it's feel.

20 or 22uf is the better choice with 2-220uf's in series for the first filter bank.

Gary

Well Gary, I guess it's back to the drawing board...again. I'm using the standard bassman caps (new Spragues). 2 20uFs in parallel for the first filter, and 20s for the others. I like the tone, and it has plently of bottom end, but maybe increasing from 40uF to 110uF may improve it a bit more? Am out of 220s for now but will give them a try. Will also have to readjust the dropping resistors. thanks for the info.