Modified #124 Schematic for review

[mauiboy81]

Thanks Heist,

That helps. Are those voltages for a non-hrm or does it matter.

I spent some time with a friend today building the cabinets. It is going to be disgusting.....in a good way. I'll post some pics when they are finished.

So do you think it could be anything else causing the 6v6's to malfunction or should i go with the short theory. If that is the case then I am very disappointed with JJ.

Any ideas about the od?

Thanks again

Nick

[heisthl]

Pi voltages should be the same for HRM and non-HRM the only time they change is for the Marshall derived "BluesMaster" PI.

Work with the 6L6es first and worry about the 6V6es later.

On an earlier post you said 42 and 45 MV readings across the 1 ohm resistors, assuming 6L6 that is too high - go for the 32 to 36 range.

Harsh is a hard term to analyze, do you mean raspy treble, edgey bass etc? Can you drastically set your tone controls to get rid of it? If so that will give the forum readers a hint at a good starting point on what areas to suggest tweaks.

[ChrisM]

Pi voltages should be the same for HRM and non-HRM the only time they change is for the Marshall derived "BluesMaster" PI.

Work with the 6L6es first and worry about the 6V6es later.

On an earlier post you said 42 and 45 MV readings across the 1 ohm resistors, assuming 6L6 that is too high - go for the 32 to 36 range.

Harsh is a hard term to analyze, do you mean raspy treble, edgey bass etc? Can you drastically set your tone controls to get rid of it? If so that will give the forum readers a hint at a good starting point on what areas to suggest tweaks.

I have my 6l6GCs at 48mA. Am I missing something, why bias so cold?

My plae voltage is 440V.

(30W)(.7)/440V = 48mA

[erwin_ve]

I don't want to cut the grass before Henry's foot, but I noticed, when biasing 6L6 really hot, the lows become very boomy.

[Structo]

Most here have said that the ODS sounds better biased on the cold side.
I agree.

[heisthl]

I have my 6l6GCs at 48mA. Am I missing something, why bias so cold?

My plae voltage is 440V.

(30W)(.7)/440V = 48mA

Where I come from we think 48ma with a plate voltage of 440 is a hot bias. but then we don't think a modern 6L6 will actually do 30 watts either.

[Sonny ReVerb]

You're right, Henry. I think I'll just sit and watch...

[heisthl]

Output tube bias has next to nothing to do with wattage once the signal gets large, it has to do with idle current.

[mauiboy81]

So, I wouldn't say the od is harsh. There is a messy kind of distortion sort of above the note that decays before the note itself. I referred to it as hash because that kind of seems like a good word for it. Any clues?

So I went to turn the amp on and there was no sound so i checked the tubes and the JJ ecc803s I had in the PI was all white at the tip and there was a small crack in the base by the pins. I am very disappointed in the quality of JJ's. What's with their quality control.

Thanks guys

Nick

[mauiboy81]

So I changed the 3.3k GNFB to 4.7k and it really livened things up. If you guys have built any 50 watters what values have you used for GNFB?

[heisthl]

with the 1uf, 4k7/390 5k1/390 and 8k2/1000. I try and pick values that create the same perceived loudness with presence on 10 (max) as GNFB not connected.

[Structo]

I have mine at 1uf, 4K7, 390 on the 4 ohm tap.

[odourboy]

I have mine at 1uf, 4K7, 390 on the 4 ohm tap.

Those are good for 100W.

For 50W, I'd suggest:

.68uF, 8.2K, 1K (2K pot) on the 4 ohm tap.

[erwin_ve]

I have mine at 1uf, 4K7, 390 on the 4 ohm tap.

Those are good for 100W.

For 50W, I'd suggest:

.68uF, 8.2K, 1K (2K pot) on the 4 ohm tap.

So for a 50 w build you would use a NFB value that's common for a 8 ohm tap?
I recently found that I have my 4k7/390 NFB at the 2ohm tap with my 50 w. (My secondary taps are 2/4/8 ohm when checking the specs of the OT... all the time I thought they were 4/8/16 ohm )
What effect does this kind of NFB have, in your opinion?

[odourboy]

Well I probably have this wrong, but my odds are 50:50....

Going off the 2 ohm tap I think will reduce the level of the feedback signal by root 2 (x.707), so you've reduced the amount of NFB.