70's fender bassman 100 head recap?

[BonesMachine]

Any esr meters cheaper than the blue one that can get the job done in circuit?

[BonesMachine]

ok so i'm just about set. i'm pretty sure the coupling caps are the 2x .1uf 600v ones connected to the 47k resistors by the phase inverter? can i get a confirmation on that?

also there are 2 more caps i'm not sure about in the same general PI area:
- 1x .1uf 200v
- 1x .01uf
do these have a name or are they referred to as anything?

[martin manning]

ine post_id=438110 time=1644544221 user_id=24033]i'm pretty sure the coupling caps are the 2x .1uf 600v ones connected to the 47k resistors by the phase inverter? can i get a confirmation on that?

Yes.

ine post_id=438110 time=1644544221 user_id=24033]also there are 2 more caps i'm not sure about in the same general PI area:
- 1x .1uf 200v
- 1x .01uf
do these have a name or are they referred to as anything?

The 0.1 is the AC ground for the non-inverting stage, and the 0.01 is the PI input cap.

[Charlie Wilson]

This is what I would do in this order:
Replace the power tubes (if they are bad), assess the output transformer, and replace obviously bad components. In other words, fix the amp.
Replace the electrolytics
Play through the amp and see what you think.
As has been stated before, the blue Paktrons are good caps and rarely have I seen them leak, the brown Paktrons I have seen a few leak but leave them if they are not.
All of the ceramics are circle D Dielectric and are very good caps. The Bassman 100 is a great amp for bass (and guitar) in its original form.
CW

[Stevem]

Since your mostly using this for guitar, once you get the amp up and running normal I would audition replacing that crappy PI input.01 ciramic cap with a .022 orange drop and at the same time replace the PI output .1 caps with .022 caps and see what you think.

[TUBEDUDE]

If replacing signal caps in a Fender, be aware the originals had metal foil construction. The CD 150 caps are of a sprayed Metalized film construction. One of the foil construcred caps may be a better fit, like the 716P orange drop, or similar.

[BonesMachine]

thanks for the info and feedback.... while i have you guys on the line. i would like to have some spare rectifier diodes on hand. what would be a good replacement part #? Thanks...

[BonesMachine]

Just wondering what caps can actually damage the amp if they are bad? I know bad filter caps can. Any others?

[BonesMachine]

The schematic calls for 3x 20uf 525v caps. They are filter caps. I can find 22uf 500v made by f&t. Will these be ok even though the voltage rating is 25v less?

[pdf64]

Dunno, that’s an engineering query in which the details of particular individual circumstances determines how things play out in various likely scenarios.
On the other hand, 550V working / 600V surge F&T KONEL22 axial caps are available http://www.askjanfirst.com/eindex.htm?/hello.htm
The caps in the bias supply are mission critical; as they fail the amp may slowly roast itself.

[Ten Over]

The schematic calls for 3x 20uf 525v caps. They are filter caps. I can find 22uf 500v made by f&t. Will these be ok even though the voltage rating is 25v less?

On a good day with all of the tubes pulled, that amp isn't going to have any more than 470V.

You have no way of knowing it, but my schematics are drawn using actual amplifiers. Those amps always have 20uF/500V filter caps in them despite what their schematic shows. How about some photographic evidence:

Doghouse 2.jpg

E Caps Removed.jpg

[Ten Over]

thanks for the info and feedback.... while i have you guys on the line. i would like to have some spare rectifier diodes on hand. what would be a good replacement part #? Thanks...

I always keep a pile of 1N4007 diodes on hand at any given time as well as MUR2100EG diodes. A lot of people keep UF4007 diodes on hand.

I wouldn't recommend fooling with the diodes unless you have a really good reason. If you just gotta, make sure to heat sink the leads in excess while soldering (as in two alligator clips instead of just one).

[BonesMachine]

There's also a bassman 100 capacitor kit sold by tube amp doctor that has the 3x 22uf 500v caps. Sounds like there's a little bit of headroom there.... I got some mini 1" solid copper alligator clips to use as heat sinks if I need em I hope they're enough. Should be able to use more than 1 or I can clip or solder together a few? also going to make some clip on test leads using them. They fit anywhere which is nice

[Phil_S]

Copper gator clips are OK if that's what you have, but solder will stick to those. It is better to use Aluminum heat sink clips like this:
https://www.newark.com/gc-electronics/9 ... t-Med-ROAS

[BonesMachine]

6.7" heat sink! nice typo newark ... on the topic of being out of spec. i've seen people use 100uf instead of 80uf for the bias caps. schematic calls for 80uf. this would make it slightly more than 20% out of spec even more if the cap is a little high. any thoughts on this? what does this do to the bias?