Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: p2pAmps on July 14, 2016, 08:55:17 am

Title: Filter cap question for AB763 circuit amps
Post by: p2pAmps on July 14, 2016, 08:55:17 am

So as I am always learning more each day about this stuff I wanted to ask for a simple explanation about filter caps on AB763 amps.

When I look at say a Twin Reverb I find 3-22uF/450v caps and 2-100uF 350v caps. 
But on a Deluxe Reverb there are 5-16uF caps and a couple of 10K resistors.

What is the reason behind the different configs?  Go easy on me guys :)

Scaggs

Title: Re: Filter cap question for AB763 circuit amps
Post by: labb on July 14, 2016, 09:03:10 am

I would venture that is because of the difference in voltage and diode rectifier and tube rectifier.

Title: Re: Filter cap question for AB763 circuit amps
Post by: p2pAmps on July 14, 2016, 09:05:40 am

Quote from: labb on July 14, 2016, 09:03:10 am

I would venture that is because of the difference in voltage and diode rectifier and tube rectifier.

So are you saying that tube rectifier 763s use the 5 16uF caps and SS rectifiers use the 22uF and 100uF?

Title: Re: Filter cap question for AB763 circuit amps
Post by: sluckey on July 14, 2016, 09:06:39 am

The TR runs higher B+ than the DR. It's expensive to use 600V rated caps. The cheap alternative is to put two lower voltage rated caps in series to increase the overall voltage rating.

The lower B+ requirements of the DR can be handled by cheap, readily available 500V caps.

It's all about economics.

As for the two 10K resistors in the DR (as compared to the 1K and 4.7K) in the bigger amps, I suppose Leo just wanted an even lower B+ for the preamps in the lower powered DR. (just a guess?)

Title: Re: Filter cap question for AB763 circuit amps
Post by: p2pAmps on July 14, 2016, 09:15:10 am

Quote from: sluckey on July 14, 2016, 09:06:39 am

The TR runs higher B+ than the DR. It's expensive to use 600V rated caps. The cheap alternative is to put two lower voltage rated caps in series to increase the overall voltage rating.

The lower B+ requirements of the DR can be handled by cheap, readily available 500V caps.

It's all about economics.

As for the two 10K resistors in the DR (as compared to the 1K and 4.7K) in the bigger amps, I suppose Leo just wanted an even lower B+ for the preamps in the lower powered DR. (just a guess?)

Thanks Steve,

I ask this question as I was doing some caps on a 68 Vibrolux and decided to use the 22s and 100s in it and added some 220k bleeders.  Well, when I fired it it had an intermittent kinda of motorboat going on.  Kinda in and out.  So I took a few minutes and put the 5 16s in it like the orig and low and behold issue solved...

Now, my latest DR with the KT66s and big iron, I used the TR type setup... no problem at all.