6g2 Brownface Princeton build

[StrummersOfThunder]

Excuse the voltages at the power nodes. I think these are the other way up fur to my on board power caps rather than cap can. Im happy with them tho I think.

[Jay]

Any of the gurus happy to check if my voltages are looking ok? There are certainly some variances to the OG schematic but from what I read that is to be expected and teh fender numbers arent gospel.

So far as biasing goes:
PC PV PD
6V6 1 - 21.6mA 308.7v 6.66w

6V6 2 23.8mA 308.2v 7.33

70% PD for 6V6 = 12 x 0.7 = 8.4

So one tube is at 55% and the other at 61% , so biased on the cool side. But safely so Im guessing?

Looking at the 6V6 datasheet for a PP class AB amp:

Plate current max is 39mA, plate V max is 315V. Plate screen max 285V. Max plate AND screen dissipation 12.5W.
Is you plate current the real plate current or does it include the screen current?
(You can calculate the screen current by measuring the voltage drop over the screen resistor and dividing that by its resistive value).

If your stated plate currents are the actual ones than yes, it is biased safely and you can go up a bit. If your stated plate currents include the screen current than perhaps rebias the amp. Don't forget the screen dissipation is limited to 2W.

If it sounds good, don't bother. Incidentally, did you buy the power valves as a matched pair?

[MikeC]

Re the 6V6s - 1. What actual make/model of tubes are they?

[MikeC]

Is the posted schematic for the amp that you've actually built?

[Jay]

Any of the gurus happy to check if my voltages are looking ok? There are certainly some variances to the OG schematic but from what I read that is to be expected and teh fender numbers arent gospel.

In terms of the other voltages the only thing significantly out of spec is the pins 1 and 6 on V1 12ax7. Fender schematic shows 135v but im getting 200v.

But the voltages on pins 3 and 8 of that tube seem to be close to correct (calls for 1.5v and im getting 1.3-1.4).

Did you put the correct plate load resistors in?

Reading the datasheet - your measurements are acceptable and the valve is still operating within its limits but the operating point at 200V sits in a more linear section of the grid curve.

[StrummersOfThunder]

Any of the gurus happy to check if my voltages are looking ok? There are certainly some variances to the OG schematic but from what I read that is to be expected and teh fender numbers arent gospel.

In terms of the other voltages the only thing significantly out of spec is the pins 1 and 6 on V1 12ax7. Fender schematic shows 135v but im getting 200v.

But the voltages on pins 3 and 8 of that tube seem to be close to correct (calls for 1.5v and im getting 1.3-1.4).

Did you put the correct plate load resistors in?

Reading the datasheet - your measurements are acceptable and the valve is still operating within its limits but the operating point at 200V sits in a more linear section of the grid curve.

They are definitely 100k

Seems as tho I’m not the only one :
https://www.tdpri.com/threads/6g2-plate ... n.1060478/

[Jay]

Any of the gurus happy to check if my voltages are looking ok? There are certainly some variances to the OG schematic but from what I read that is to be expected and teh fender numbers arent gospel.

In terms of the other voltages the only thing significantly out of spec is the pins 1 and 6 on V1 12ax7. Fender schematic shows 135v but im getting 200v.

But the voltages on pins 3 and 8 of that tube seem to be close to correct (calls for 1.5v and im getting 1.3-1.4).

Did you put the correct plate load resistors in?

Reading the datasheet - your measurements are acceptable and the valve is still operating within its limits but the operating point at 200V sits in a more linear section of the grid curve.

They are definitely 100k

Seems as tho I’m not the only one :
https://www.tdpri.com/threads/6g2-plate ... n.1060478/

Indeed, shows a nice marked up circuit diagram with voltages.

Assuming your cathode resistor is 1500 ohms then your cathode current is 0.8ma. That will cause a 86V drop over the 100K load resistor. Does that stack up to the supply voltage (200V + 86V) to that stage?

[StrummersOfThunder]

Did you put the correct plate load resistors in?

Reading the datasheet - your measurements are acceptable and the valve is still operating within its limits but the operating point at 200V sits in a more linear section of the grid curve.

They are definitely 100k

Seems as tho I’m not the only one :
https://www.tdpri.com/threads/6g2-plate ... n.1060478/

Indeed, shows a nice marked up circuit diagram with voltages.

Assuming your cathode resistor is 1500 ohms then your cathode current is 0.8ma. That will cause a 86V drop over the 100K load resistor. Does that stack up to the supply voltage (200V + 86V) to that stage?

Yep that sounds about right for my B+ at the preamp node

[StrummersOfThunder]

Bit of a shoutout to @starfire for the logo
Sandy at emblems did a fine job on this and the deluxe face plates.

[StrummersOfThunder]

Rob and I tested this (and the 6g3s) thru a range if speakers today.
What I will say as this is a cool little beastie. It definitely has a foot planted in both tweed and blackface camps. It is assuredly brown but has a wonderful sparkle to it. And very pleasingly it avoids the dreaded fizz that the blackface princeton can get when pushed.
My preference was for the jensen jet alnico but Rob clearly preferred the cream back. I would say the cream back accentuates where the jensen tames, i.e if you want to declare that your packing brown then the cream back is your friend. The trem is particularly sweet.

Prior to testing I put in a NOS 573 and biased the set of cork sniffy NOS RCA 6v6s that Grant posted up. Happy to say all tubes survived and no lead sarcophagus was required. I used my current limiter as Im still a little gun shy after the assisting dieing of Grants other 573.

I like this 6g2 so much im fairly sure im going to build one for myself.

[Bg]

Still awaiting delivery of bits... but I can confirm 2 cabs are pretty much done otherwise

[StrummersOfThunder]

Still awaiting delivery of bits... but I can confirm 2 cabs are pretty much done otherwise

Awesome
They have been sent ! Robbie gave me a tracking number I think ….

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xmas post, all good fun

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IMG_1803.jpeg (2.89 MiB) Viewed 2380 times

[robthemac]

Chocolatey.