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[Gregg]

Some time ago there was a discussion about that 12V power supply and the consensus was R381/R382 must be removed.
I've used this voltage doubler in...

[Gregg]

NO!...

[Gregg]

COP = coefficient of performance.
Every device has a COP which is never 100%. OTs are no exception.
When determining the turns ratio and the impedance...

[Gregg]

It''s the standard. Pin 1 is the lower left corner when facing correctly what's printed on the IC....

[Gregg]

If you run DC heaters on the first tube only you can use this corrected schematic from Mark IV without adding another PT. I've used this many times and it...

[Gregg]

You can do both together. In high gain amps I do all preamp tubes DC (12V regulated) but I have a dedicated 15V secondary. In most cases the first 2 tubes...

[Gregg]

I always use transformers with dedicated bias secindary and never use it for anything else unlike for example mesa where you can see all kind of voltages...

[Gregg]

I didn't. 10uF is more than enough.

I'm with you about the divider values. Sometimes if you don't know how to do it look how the "big ones"...

[Gregg]

https://ohmslawcalculator.com/voltag...der-calculator



Schematic (JVM410) was posted above. It doesn't get more simple than that....

[Gregg]

It looks like this one will be able to do 6 preamp tubes in 1U rack:

https://www.tube-town.net/ttstore/to...30va-8808.html

Use...

[Gregg]

That's not possible unless:
1/ you have broken ground
2/ your measurements are not correct (for example not with respect to ground)...

[Gregg]

That must be a mistake otherwise it doesn't make sense....

[Gregg]

There should be ~12V at FETs' gates otherwise the FET will be "closed" (low source to drain resistance effectively in mute state).
The TVS...

[Gregg]

There are 2 mute FETs on page 4 of the schematic. Those are Q3 and Q6. Q3 is the "main" mute FET and if blown would affect the overall volume. Q6...

[Gregg]

I had several Mesas on my bench with low volume issues and in most of them the culprit was a blown mute FET so make sure to check those as well.

[Gregg]

This is entirely true. Below is an interesting article about tapers of some well known HiFi pots together with an Excel table with graphs:

h...

[Gregg]

Couple of years ago I spoke with a Song Huei distributor in Europe and they had a minimum of 200pcs for any custom taper, lead time 8 weeks but I don't have...

[Gregg]

According to ALPHA RV16 series pots datasheet D taper is 10% log taper. Also note the G taper which is 5% log taper. Used as Gain pot in Mesa DR and Gain...

[Gregg]

Don't forget to install those grid stoppers as recommended on the last page....

[Gregg]

CD4028 can do 3 and 4 channel switching.

And another one with 4011....

[Gregg]

You're right. I just saw the "0V" references and didn't follow further.


In my practice I never observed hum in a DC floating...