Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: aabbs20 on December 27, 2019, 09:57:11 am

Title: 6L6 AB763 Reverb in a Princeton Chassis
Post by: aabbs20 on December 27, 2019, 09:57:11 am

Hey all! 

I'm thinking of building a single channel 6L6 AB763 style amp without the trem.  I have a few Princeton chassis around and was hoping to fit everything in there.  If I used an Allen TP25 (310-310@150ma) and TO35MT what type of output wattage should I expect? 30 or so?

http://www.allenamps.com/trans.html

Thanks as always,

Aaron

Title: Re: 6L6 AB763 Reverb in a Princeton Chassis
Post by: SILVERGUN on December 27, 2019, 10:48:10 am

30 or so is a good guess-timate.
This is a solid plan that has been done before and will fit nicely in a Princeton chassis.

If you want to save a couple bucks on the PT and yield a slightly higher B+, I have been using these for this platform: https://www.hammfg.com/part/290CX
This does require enlarging the PT hole on a standard pre-punched chassis.

https://www.angela.com/hammondpowertransformer290cx.aspx

Title: Re: 6L6 AB763 Reverb in a Princeton Chassis
Post by: SILVERGUN on December 27, 2019, 11:04:27 am

One thing to keep in mind with an upgraded PT in a small chassis is the distance between it and the rectifier/power tubes.

I remember running into this issue the fist time I did it and making a mental note to move the enlarged hole towards the front panel as you can see in this drawing.
The yellow arrow points to the side of the PT that should be moved forward. I highly suggest moving the PT this way for clearance. I remember one of my power tube clamps was right up against the PT.
This is an actual pre-punched Princeton chassis in this pic.

Title: Re: 6L6 AB763 Reverb in a Princeton Chassis
Post by: DummyLoad on December 27, 2019, 12:01:22 pm

cathode biased EL34 with 450V B+ into 6.6KRa-a load will net about 40W. if you use the allen TP26, it is a 7KRa-a part, so slightly less.  Rk for each EL34 will need to be around 470R @ 10W or >. use 1K 3W or > screen resistors. full power demand would be around 180mA for just the output stage. EL34s suck more screen current than 6L6 do, so you may wish to consider use of the 90mA fender choke. 


that's what i'd shoot for.


--pete

Title: Re: 6L6 AB763 Reverb in a Princeton Chassis
Post by: aabbs20 on December 28, 2019, 09:05:16 pm

Thanks for the tips guys!

Title: Re: 6L6 AB763 Reverb in a Princeton Chassis
Post by: glass54 on December 28, 2019, 11:24:59 pm

Hi aabbs,
Do it  :laugh:. I used a Princeton Tweed case with my own chassis and a Hoffman AB763 Turret board with 6V6s, Rev and Trem. I had a custom Toroidal Tx suitable thus no Rect Tube. I'm getting 21.5W of pure sinewave (1kHz) thus a Princeton on Steroids  :l2:
(Officially my personal first build, although I have rebuilt amps for others) See attached Pix.

Kind Regards
Mirek

Title: Re: 6L6 AB763 Reverb in a Princeton Chassis
Post by: glass54 on December 28, 2019, 11:26:28 pm

...and a completed shot. (may do a custom front panel later)