Re-Caps for my 1963 Brownface Bassman

[Johnny1958]

Hi All, I want to update my 63 Bassman, when it is on for over an hour, it has a low pitch Shhhhhhhhh noise coming from it, and i suspect the capacitors.
I know there are the bigger ones under a separate cover, and some others smaller ones on the wired board.
I use the amp in my rockabilly swing band, the sound texture is killer.

How should i look at this, i donno what be best to do. should i replaced the high section, or all of the electrolitics ? brand? etc..

There are some pictures of it in my photo album.

That would be a good entry level to update my amp. I'd like to build amps later on, i'm nutz about sound
Many Thanks

[txstrat]

From the "Shhhhhhhh" in your post I'd assume it's more a hiss than a buzz or hum, right?
If it's a hiss I'd suspect the carbon comp resistors. These can start hissing when getting old.
If it's more like a hum or buzz it might be the caps only.
If the caps haven't been changed yet it's probably time for them anyway.
If you're familiar with a soldering iron you can just replace the components for parts with the same values. Use quality parts like Sprague Atom caps and/or carbon film (or metal film) resistors. (The amps board won't look as vintage anymore but usually you wouldn't keep the amp open while you play, would you? )
IMPORTANT
Don't forget to drain the old caps before you touch them. They contain LETHAL voltages even when the amp's been off for quite a while. I usually use a 10K/1W resistor from the + of the cap to ground to drain the voltage.

And welcome to the forum.

[BiBi]

Hi I had a look at your photos and those electrolytic capacitors under the cover definitely should be replaced. The most important part of the task is making sure that the voltage rating on the capacitors is high enough. I notice that yours currently are rated at 525V which is probably very close to what the power transformer is putting out. This means the capacitors will not last as long and be more subject to failure. Of course yours already lasted nearly 40 years so that may seem dead wrong but you may have been lucky I don't know...
If it's your first time doing all this I would personally recommend finding a friendly tech in your area who will let you look over their shoulder. It's not a difficult job but it can be deadly.
My preference would be to replace one thing thing at a time i.e. replace the capacitors before the resistors. The new capacitors will change the sound quite significantly-- more bass, less noise-- already so you may want to concentrate on that first. Resistor drift is not that serious usually and changing those can't be justified as easily when reselling vintage equipment.

[MWJB]

Easy option - replace the caps in the pan with F&T 20uf 550v caps from TAD, these will handle the voltages in your amp and be the simplest replacement. For best tone however, I'd rewire the main filter caps (the 2 in parallel, nearest the power tubes) with 2x100uf 350v Sprague, or 2x220uf 350v F&T caps in series, each cap bypassed with a 220K 2W resistor. You will need to remove a jumper under the cap board at the positive ends of the main caps, so that the new caps can go in series (not parallel like the old ones - see how the Super Reverb caps are wired), you will have to move the ground (black) wire that connects to these caps to the "-" terminal of the 2nd series cap.

20uf 500v/550v volt will be fine for other positions in the cap pan.

Replace the preamp cathode bypass caps (12AX7 pins 3 & 8) with Sprague 25uf/25v. Thes will be single caps, 2 will need to replace each "double" cap (2 positive terminals) on the board.

Replace the bias cap, up by the power transformer, near the pilot lamp, with a 100v cap, not a 50v cap. 100uf/100v are commonly used here & sold everywhere.

You are free to use cheaper Asian caps (Mojotone sell TAD Chinese caps), uf & voltage rating are the most important aspect, but if you come to sell the amp prospective buyers will want to see "guts shots" before commiting, recognised brands will give them better peace of mind.

Bring the amp up gradually on a variac or use a lightbulb limiter, monitor voltages & plate current before running straight into the wall AC.

[Johnny1958]

From the "Shhhhhhhh" in your post I'd assume it's more a hiss than a buzz or hum, right?
If it's a hiss I'd suspect the carbon comp resistors. These can start hissing when getting old.
If it's more like a hum or buzz it might be the caps only.
If the caps haven't been changed yet it's probably time for them anyway.
If you're familiar with a soldering iron you can just replace the components for parts with the same values. Use quality parts like Sprague Atom caps and/or carbon film (or metal film) resistors. (The amps board won't look as vintage anymore but usually you wouldn't keep the amp open while you play, would you? )
IMPORTANT
Don't forget to drain the old caps before you touch them. They contain LETHAL voltages even when the amp's been off for quite a while. I usually use a 10K/1W resistor from the + of the cap to ground to drain the voltage.

And welcome to the forum.

Thanks All for the quick reponse and warm welcome

Hi txstrat, Yes the noise is more a "hiss" as there are no audible pulse to the sound.
I'm very manual, and soldering and unsoldering is no problem for me.
I was aware of caps holding charge, but didn't know the best way to drain them out. I'll use a 10K/1W resistor and close circuit them all to be safe.

I did use a Sprague as a treble bleed on the master volume of my Gretsch

[Johnny1958]

Hi BiBi, the caps do look like they have been replaced (under the cover) the other ones looks original, i think i'll change all the electrolitics.
With some guidance, i think i can do it no probs.

But i didn't know by changings the caps it would change in sound.
Does that mean that it will sound closer to like it was new? "bout tone?
It really sounds great as it is, i wouldn't want to move too far from that tone ( not that i have a choice!!! ) Hope it's for the better

[Johnny1958]

Hi MWJB, 1st thanks for the link up to TAD and telling me about the F&T brand from Germany

I will replace the big caps under the cover with Sprague Atom 20uf 500v
if i can still find them.

I will study closely your suggestions for the other caps, as to make sure i understand all clearly.
I also do have the schematic here someplace in my comp.

i know there were 2 different circuitry in these.

pasted:
6G6
(1961-1962) 4 x 7025
2 x 5881 Odd circuits aplenty. DC coupled first gain stages, cathode-driven 'Bass' control in 'Bass' channel. 'Treble' control is after 3rd gain stage. Tapped 'Treble' control in 'Normal' channel.

6G6A
(1962-1964) As above. As above, with linear-taper 'Volume' control in 'Bass' channel. Also, has more inverse feedback.

6G6B As above. As above, with slightly different tone controls in 'Bass' channel.
end

I'll try to see which of the two i have. i have seen a litle "a" on the wired board written by hand, but i dont think i should assume by that.

[stokes]

Johnny,changing those filter caps will change the response of the amp more than the tone,which could be percieved as "tone change",but I think you will like it.It will improve the bass response the most,you will lose any flubbiness,if you will,in the bass.Those caps are old and likely not supplying the power your tubes need quick enough.As caps degrade most people dont notice it because they do so gradually so the degradation in tone or response happens slowly and you become accustomed to the amp as it is at the moment until it begins making noises that point you to the filter caps,that "hiss".It is important to change them because when they get this old they are at risk of shorting or worse expelling their guts,not good.The amp will feel much tighter and solid with crisp cleans,it may or may not break up a bit later,but it will still break up nicely with a much "broader" touch response,you wont be sorry,you may think it sounds good now,and it does,but you will be amazed at how much room for improvement there really is.

[Johnny1958]

Holly Gee!!! I can't wait to hear that difference, i'm gonna start choppin around for the caps. when i get into the doin', i'll sure upload my progress with pics
Thks All

[MWJB]

"But i didn't know by changings the caps it would change in sound.
Does that mean that it will sound closer to like it was new? "bout tone?" It will sound like it works properly, the other benefit is that the new caps won't go up in a cloud of smoke halfway through a set. I have never had a customer be dissapointed with the tone of a properly serviced vintage Fender.

[Resonator Guy]

You can get those Sprague Atom 20uf@500v at Antique Electronic Supply.
Antique Electronic Supply

[Johnny1958]

"But i didn't know by changings the caps it would change in sound.
Does that mean that it will sound closer to like it was new? "bout tone?" It will sound like it works properly, the other benefit is that the new caps won't go up in a cloud of smoke halfway through a set. I have never had a customer be dissapointed with the tone of a properly serviced vintage Fender.

If any cares to hear its sound texture, here is my band page, did the recordings about a year ago.
Gretsch 6119 Tennessee Rose into my Roland Re-301 Space Echo into the normal channel, vol 4 1/2 - bass 5 - treb 7- presence max : )P

these are StrayCats covers exept cuisin' low.

all recording done in unfinished basement with a ciment floor.

The SpaceBillies on MySpace Music - Free Streaming MP3s, Pictures & Music Downloads

Lemme know what you think of its sound

[Johnny1958]

You can get those Sprague Atom 20uf@500v at Antique Electronic Supply.
Antique Electronic Supply

Great shop, thnks for the link Resonator Guy

[Johnny1958]

Hi All

I'm getting my list ready now that i can afford the expense! (times are a bit tough round here lol )

hope i'm getting all i'll need:

2x 10k 1w resistor/ safty bleeder (carbon or ceramik?)

Metal box cover:
5x Sprague Atom 20uf 500vdc

Board:
4x 25uf 25vdc
2x 25uf 400vdc
1x .047uf 400vdc (smaller body)

4x .lmfd 400vdc (not sure of this value? .lmfd is it .1 mfd?)
1x .lmfd 200vdc (not sure of this value? .lmfd is it .1 mfd?) also smaller body

Off board:
1x 100uf 100v (bias)
1x .047uf 600vdc (ground)

Do you figure i'm on the right track?

I highly appreceiate any and all help you can spare
Sorry for my Newbility

[txstrat]

2x 10k 1w resistor/ safty bleeder (carbon or ceramik?)

If you want to put them parallel to the filter caps - I usually use 220k 2W metal film.

4x .lmfd 400vdc (not sure of this value? .lmfd is it .1 mfd?)
1x .lmfd 200vdc (not sure of this value? .lmfd is it .1 mfd?) also smaller body

.1uF and .1 mfd is the same = microfarad

Off board:
1x 100uf 100v (bias)
1x .047uf 600vdc (ground)
Do you figure i'm on the right track?

Yes