Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: firemedic on March 11, 2011, 02:58:03 pm

Title: Tremolux Reverb build is done
Post by: firemedic on March 11, 2011, 02:58:03 pm
I couldn't think of a better name for it.
This amp has the best clean tone I have yet been able to produce. The heart of it is a BF Pro Reverb AA165 reverb/vibrato channel.
The normal channel is a 5879 stage with the exact same component values as geezer's HoSo56, into a standard BF tonestack. The 2nd stage of this channel is 1/2 of the reverb send 12AT7 (V3b). By feeding this stage into the grid of V4b thru 3.3M/10pF, just like the reverb channel, normal/reverb channel bridging is possible without phase cancellation and it sounds GREAT. Thanks to Gerald Weber for that idea.

The power section & tremolo circuit are copied from the Hoffman AB763. So the power tube bias-vary tremolo works on both channels. I experiment with different output tubes frequently so I mounted the bias pot externally and it is a 10k/10 turn affair.
The B+ power rail has 7 nodes instead of the stock 4. I needed to drop some voltage to the 5879 to keep it within max specs.

12AY7s in V2 & V4 and a 12AT7 driver, instead of 12AX7s. This is a powerful amplifier (for me) and it was losing some character with all that gain.
There is also a 5k NFB cut pot. Pentode-triode switch. GZ37 rectifier.
You guys helped a LOT letting me bounce ideas off you. In fact I would have no good amps at all if not for this forum. I'll post the schematic when that's done.
Title: Re: Tremolux Reverb build is done
Post by: Cups on March 14, 2011, 10:49:00 am
Schematic and pictures would be fun.  :icon_biggrin:
Title: Re: Tremolux Reverb build is done
Post by: firemedic on March 14, 2011, 10:53:14 am
Stand by on that. I'm even slower on the keyboard than I am on guitar.....
Title: Re: Tremolux Reverb build is done
Post by: firemedic on March 15, 2011, 05:28:01 pm
Here's the preamp schem anyway. I'm still doing the power section part, it's the Hoffman AB763 Vibroverb power section with a couple of power nodes added. Still trying to get the photos to post...
Title: Re: Tremolux Reverb build is done
Post by: firemedic on March 15, 2011, 05:34:50 pm
aaaaaand the grainy photos.
Title: Re: Tremolux Reverb build is done
Post by: firemedic on March 15, 2011, 06:10:41 pm
Here's the power section schem. I didn't even write down my voltages before putting it in the cab. I know the plate voltage is 430V, and the supply node (G) to the 5879 is 298vdc, just within the 300v max... Biased 40mA per tube. Every other nominal voltage is about what you would expect, nothing unusual or crazy.
Also I should have noted that the V3a (reverb send) cathode is grounded at the star ground point & not at the preamp ground, to avoid potential oscillation. That's a Weberism.
I did just realize the cathode resistor there is too small & the tube is probably drawing too much current. Do I have to take it apart AGAIN?
Title: Re: Tremolux Reverb build is done
Post by: tubenit on March 16, 2011, 08:27:03 am
That is a very cool amp!  Thank you for sharing the schematic for it.

With respect, Tubenit
Title: Re: Tremolux Reverb build is done
Post by: firemedic on March 16, 2011, 12:24:14 pm
Thanks, any thoughts on the possible V3a current/cathode resistor issue?
Title: Re: Tremolux Reverb build is done
Post by: EW57 on March 18, 2011, 12:03:14 pm
Sorry for the derail/dumb question, but what is used to view .sch files? Thanks!
Title: Re: Tremolux Reverb build is done
Post by: sluckey on March 18, 2011, 12:34:52 pm
Quote
what is used to view .sch files?
Check this...  http://www.el34world.com/Forum/index.php?topic=500.msg831#msg831
Title: Re: Tremolux Reverb build is done
Post by: EW57 on March 18, 2011, 06:44:55 pm
Quote from: sluckey on March 18, 2011, 12:34:52 pm
Quote
what is used to view .sch files?
Check this...  http://www.el34world.com/Forum/index.php?topic=500.msg831#msg831


Thank you sir!  Looks like I'm >4 years behind the curve, just like my schooldays!