Tremolux 5G9 adjustable bias w/HV tap

[Diverted]

Hi,

I would like to start building a Tremolux 5G9, which has non-adjustable fixed bias and uses a 50V bias tap off the transformer.

The transformer I am using does not have a bias tap so I'm tapping the HV secondary. Can anyone look at the schematics and tell me if I've got this right?
Included are:
First: Original schematic
Second: Drawing of original schematic
Third: Drawing of proposed schematic with bias pot.

Thanks!

[pdf64]

That should be fine.
The bias supply feeds the depth pot, not the speed though 
Bear in mind that as the values are fairly low, film caps could be used in the bias supply.

[Diverted]

Gah! Sorry, that one's a typo. Don't want to know what would happen if I wired to depth

[Willabe]

I built that amp and LOVE it!!!! I'm not a heavy distortion guy, that amp has a very nice clean to nice breakup sound. And the trem is great, if you like trem. I like waaayyy better than my 5E3 clone.

I used Mercury Mag iron, I've bought enough of their iron to get a pretty decent discount.

[Diverted]

Nice! A friend of mine owns one and it’s a really great amp. I’m using a 300-0-300 transformer@144ma so that should do nicely.

Did you build the cab to spec? (That is, big)?

I built that amp and LOVE it!!!! I'm not a heavy distortion guy, that amp has a very nice clean to nice breakup sound. And the trem is great, if you like trem. I like waaayyy better than my 5E3 clone.

I used Mercury Mag iron, I've bought enough of their iron to get a pretty decent discount.

[Willabe]

Did you build the cab to spec? (That is, big)?

Yes and that's part of it's sound.

The larger cab size than a tweed deluxe gives it a little more bottom end and low mids.

[sluckey]

I like to plagiarize. Look at page 4...

     https://el34world.com/Hoffman/files/Hoffman_PrincetonReverb.pdf

[Diverted]

Thanks Sluckey.
Any ideas why Fender went with a bias circuit for this amp different than the one seen on Princetons and Blackfaces, and on your schematic? Just an earlier design that used an extra filter (expensive)?

I'm assuming that functionally there would be no difference between the two, as long as it's supplying filtered negative voltage. Right?

Thanks!

[tubeswell]

See how you go. If the 100k dropper off the 300-0-300 HT results in a bias voltage that’s too low, you could always try 82k or 68k etc

[Diverted]

I have a question about the 2m speed pot in this amp. Type isn't listed on schematic but it appears to be a reverse audio taper. I'm having a tough time finding one, but I do have a bunch of CTS 3mra taper pots in my drawer.
Can I get away with this pot?

[sluckey]

yes

[Willabe]

Diverted, here's the link to my 5G9 build. It's 2 1/5 pages, so not too long. Might be helpful to you?

I had a problem with most likely the LFO tube socket and I had to get rid of the bias/balance, it was changing the -bias when I turned the depth pot.

There's my schematic and layout drawings in there, with elevated heaters. Several pics of the chassis loaded, eyelet/turret board. 

Good stuff in there from Sluckey, HBP, tubeswell, dummyload, etc.

https://el34world.com/Forum/index.php?topic=13912.msg130498#msg130498

[Diverted]

Thanks for the help everyone. Finally got to powering up the amp today and wow, I'm impressed. It's like a cleaner, tighter and warmer Deluxe. The tremolo is wonderful.
Only hiccup along the way was very, very low output on initial startup, and a few voltages way off. Traced it down pretty quickly by reviewing everything. Somehow a 470K resistor ended up in my 470 ohm drawer. No wonder there was an issue with a PI cathode resistor 1000x the correct size 
After I fixed that issue all the voltages are within 5-10vdc of spec, at 122VAC house voltage.
Next up, a cab. I'll build that to spec'd size, planning on either a Celestion Blue (15w) or Celestion Ruby (35w). Blue slightly underpowered at the 18w the amp puts out full out, and the Ruby slightly over. I probably will never crank this one full out so I will probably go with the blue.

Thanks again. Yeah, my bench is messy, it's always a disaster by the end of a project.

[Willabe]

Did you build the cab to spec? (That is, big)?

I should add;

I built the amp after reading about it Tone Quest Report magazine. They had bought 1 and reviewed it. They LOVED it!

They said Fender put that amp in a tweed Pro cab, which is larger than the tweed Deluxe cab. They loved that Fender used the Pro cab, said it was fuller, had more bottom, low mids, because of the cab, than a tweed Deluxe 5E3. The Pro did come with a 15" speaker, hence the larger cab, the 5G9 had a 12".

From Mojo tone;

Tweed narrow panel Pro; H 21" x W 22 1/2" x D 10 3/8"

Tweed narrow panel Deluxe; H 16" x W 20" x D 9 1/2" 

[Diverted]

They said Fender put that amp in a tweed Pro cab, which is larger than the tweed Deluxe cab. They loved that Fender used the Pro cab, said it was fuller, had more bottom, low mids, because of the cab, than a tweed Deluxe 5E3. The Pro did come with a 15" speaker, hence the larger cab, the 5G9 had a 12".

From Mojo tone;

Tweed narrow panel Pro; H 21" x W 22 1/2" x D 10 3/8"

Tweed narrow panel Deluxe; H 16" x W 20" x D 9 1/2"

Thanks Willabe. Yes, I can confirm it's an enormous cabinet. Mine's 22x20x10.5 deep tapering at top to 9.25.
Tremendous, deep bass that stays tight, beautiful tremolo. Can't wait to break in the speaker. And I'm really glad it's dead quiet and hum-free, one of the quietest amps I've heard much less built.

[Willabe]

Looking good! 

Where did you get the chassis? A Hammond blank? You make it?

[Diverted]

Thanks! Yep, a Hammond steel blank. I like them, use them all the time.