Old white mallory electrolytic caps..no capacitance ratings..any advise?

[ctcpete]

Hello all, I'm a new member. I have begun a refurb and blackface conversion of my '73 Twin Reverb. Some of the white Mallory electrolytic caps are only labled with a voltage rating, no capacitance rating unless I don't understand the code. iene is labled 5-50VDC, 088567, 2357341KA. I havce tried to google old Mallory codes etc with no success. Even the schematics I have found easily on the internet only have voltage ratings on them for these particular caps. I believe it is the AA270 circuit, any advise?
Thanks, Pete

[Bruce / Mission Amps]

Hello all, I'm a new member. I have begun a refurb and blackface conversion of my '73 Twin Reverb. Some of the white Mallory electrolytic caps are only labled with a voltage rating, no capacitance rating unless I don't understand the code. iene is labled 5-50VDC, 088567, 2357341KA. I havce tried to google old Mallory codes etc with no success. Even the schematics I have found easily on the internet only have voltage ratings on them for these particular caps. I believe it is the AA270 circuit, any advise?
Thanks, Pete

Simple, replace them all with any generic axial electrolytic capacitor with a rating of 22uF@50vdc... with respect to the 5uF at 50v cap in the vibrato circuit, I always use a 4.7uF@100v cap there.

[ctcpete]

Thanks for the info Bruce. There where two other white mallorys labled 80-75VDC, 003994. Any advise on these?

Thanks again for your help.

Pete

[Bruce / Mission Amps]

Thanks for the info Bruce. There where two other white mallorys labled 80-75VDC, 003994. Any advise on these?

Thanks again for your help.

Pete

Use two, 100uF@100v.. those are the bias supply filter caps.

[ctcpete]

Thanks again Bruce. I wonder why Mallory would list capacitance values on some of their caps from that era but not on others. I was especially discouraged when the schematic also didn't call out any capacitance ratings. Maybe they where thought to be "a given"?
I was a tech for many years in the printing industry (unfortunately I am a recent victim of the economy) but have very little experience with tube amps. I am now just getting into working on my own amps as I have the time to do it now. I am finding lots of great info on the internet. This is a wonderful site, it seems like a lot of good people participate. I also just posted on my Blues Junior in the mods section. Thanks again for the good advise.
Regards, Pete

[Enzo]

5-50v means 5uf at 50v

80-75v means 80uf at 75v.

We assume the capacitance of an electrolytic like that will be in microfarads, not picos.

[ctcpete]

A HA! Thanks very much for the info.

[spiral]

with respect to the 5uF at 50v cap in the vibrato circuit, I always use a 4.7uF@100v cap there.

Are you talking about a cap on the vibrato pedal switch jack sleeve? I have '71 silverface deluxe reverb and don't know if i need to replace a cap that goes from pin 3 of the 12ax7b @ V5 to the sleeve of the vibrato switch jack.

I bought a set of caps to redo all the never-replaced filter caps in my amp, and i am replacing with Blackface specced parts, using the Weber 6a20 drawing as a guide. Problem is, i have 1 extra cap which is 22uF@100v, which brings me to my actual question:

I have an extra 22uF@100v cap from a blackface cap kit and am wondering what it replaces. The only remaining white mallory cap is the 25uF@25v, mentioned above, that attaches to the vibrato switch. The value of my new cap doesn't match the existing one and there is no cap present at that location in the Weber drawing.Should the new 22uF cap go somewhere more important, like to filter audio somewhere else? Does this vibrato switch cap need to be replaced?

The only other place i thought it might be for is behind the lamp, there is what i assume is, the bias circuit which has a large metal 50uF cap (but this value matches the Weber schematic).

I'm new both on this board and to modding/repairing my amp.

[ctcpete]

Hi Spiral I'm also a newbie to tube amps but have had good success modding two of my amps thanks to this forum and info on the web, the caps I where asking about (on my 74 Twin Reverb) where the bias circuit caps (near the lamp on the small board that connects to the hum balance pot and the zener diodes. I recommend if you don't have good schematics refer to these sites I'll try to post the links or just google fender schematics.

I got into some trouble while I was blackfacing my twin and got a little lazy( I usually have my laptop with schematics available) and tried to do some of the mods using only Weber's instructions from his book which has a chapter on blackfacing a twin. He did not mention any of the Master Volume circuitry or refer to it in his drawings. Caused me some complications which I corrected by spending time with the drawings and schematics. Which silverface Fender are you referring to?

Most important, are you aware of the safety considerations for working in a tube amp? Capacitor discharging, safe biasing procedures etc? Lethal volatages are lurking around.

I'm a little short on time now but suffice to say there is lots of good info on the web if you have the time to hunt around a liitle I have lots of other links for parts and info as well. See my links for schematics and layouts. Also check out Hoffman amps library for good Fender info. Feel free to contact me for other links. Other guys / Gals here have tons of experience.

http://www.schematicheaven.com/fender.htm

[ctcpete]

Spiral here's another one. Also, Webers website has a phone # listed, there is a tech support person there )(at least when I called) I decided to purchase parts myself. Mouser and Antique electronics parts are decent sites.http://http://www.thevintagesound.com/ffg/

[spiral]

Thanks for the lengthy reply. I have been reading non-stop for two weeks to absorb all i can while i do the modifications, and this board is great. At this point i plan to do it in stages so if something went wrong, i don't have to troll through 10 different types of changes. First step is just replacing the filter caps and the bypass caps. 90% of them are direct swaps. The only question i had was about the different values of the filter caps between SF and BF. I have since found out that my specific SF has the same transformer as the original BF. Mine is a 1971 Silverface, and so far there are very few things that were changed based on the BF drawing im looking at. Before i did any of that i clipped the .001 caps from the power tubes and it really did open up the sound.

Hi Spiral I'm also a newbie to tube amps but have had good success modding two of my amps thanks to this forum and info on the web, the caps I where asking about (on my 74 Twin Reverb) where the bias circuit caps (near the lamp on the small board that connects to the hum balance pot and the zener diodes.

I had similar white mallory bypass caps that i have already replaced. I also have a metal can mallory cap which is for the bias circuit (i had my SFDR modded so it has a proper bias pot) and is supposedly specced lower than it should have been. Original BF amps had 50v caps there. Mine has a 50uf@70v as stock. I ordered a 100uf@100v to replace it, based on the consensus of a few guides and individuals. (i still can't figure out what this 22uF@100v cap was intended to replace.)

I recommend if you don't have good schematics refer to these sites I'll try to post the links or just google fender schematics.

I have been using the Weber 6a20 combo drawings. They are great because they are colored, and are layout drawings as well as schematics.

Caused me some complications which I corrected by spending time with the drawings and schematics. Which silverface Fender are you referring to?

Yeah just from looking at the layout and studying the drawing i'm starting to get a feel for the signal flow and what bits do what. My Silverface is a 1971 Reverb Deluxe ("wired by M. Torres 1971" stamped inside)

Most important, are you aware of the safety considerations for working in a tube amp? Capacitor discharging, safe biasing procedures etc? Lethal volatages are lurking around.

Indeed! I made a cap discharge wire with a 10k resistor. I know that from working with other analog gear, but was doubly cautious since the voltages are higher.

I'm a little short on time now but suffice to say there is lots of good info on the web if you have the time to hunt around a liitle I have lots of other links for parts and info as well.

Thanks again so much! Feel free to post them.

[ctcpete]

Spiral, If you purchased the kit from Weber, why don't you just call them and ask them about the mystery cap.
If it is for a blackface kit it may be the reverb cap located on my twin on the back near the reverb plugs.

[spiral]

Spiral, If you purchased the kit from Weber, why don't you just call them and ask them about the mystery cap.
If it is for a blackface kit it may be the reverb cap located on my twin on the back near the reverb plugs.

Kit was from Torres and yes i need to call them. I'm just trying to kill too many birds with one stone (learning about the caps and values and what should and shouldn't be swapped) and have been putting it off. Damn you and your common sense.

[spiral]

Spiral, If you purchased the kit from Weber, why don't you just call them and ask them about the mystery cap.
If it is for a blackface kit it may be the reverb cap located on my twin on the back near the reverb plugs.

It was actually on the receipt as a bias cap but i ended up not using it and replacing it with a higher voltage one based on recommendations here. Thanks!