bandmaster rectifier diode type?

[r0bo01]

as far as i can google it, 1n4007 seems to be the diode for my bandmaster bf's rectifier bridge. does this sound right?
schematic calls for 330v to rect. bridge (6 diodes), 440 v to 6l6 plates.
amp uses 7025 (2) preamp, 12ax7 (1) vibrato, 12at7 (driver?) & 6l6gc (2) power.

i bought one of those kits w/100uf 450v sprague atoms for filters, etc. any problems there?

thnx for any responses in advance...

[Manic]

I'm no authority but.....

Originally Posted by r0bo01

as far as i can google it, 1n4007 seems to be the diode for my bandmaster bf's rectifier bridge. does this sound right?

Yes, I wouldn't replace if their working.

Originally Posted by r0bo01

amp uses 7025 (2) preamp, 12ax7 (1) vibrato, 12at7 (driver?) & 6l6gc (2) power.

Yes, a 7025 is a 12ax7. Back in the day it was a heavy duty 12ax7, more resistant to microphonics. Also said to have slightly different tone.

Originally Posted by r0bo01

i bought one of those kits w/100uf 450v sprague atoms for filters, etc. any problems there?

I dont think a little over filtering of a diode based rectifier will hurt anything. Tube recto is a different story. They have limits. Power tranies using SS or tube recto's have limits as well. Going from 30uf to 50uf (series caps) should be fine.

If someone would confirm My answers that would be awesome!

FWIW C. Smith

[hollisdevillo]

yes 1n4007. good. tubes are good. most recommend to up the two original 70mf caps to 100mf. they add the nice bottom end and smooth out filtering better. leave the 20's as 20's, though. this is a a silverface i presume because of the extra 12ax7. i would consider blackfacing it. fender put in the lame balance bias pot, among some other stupid changes which sucks tone out of the amp.

[gldtp99]

Yes, 1N4007 diodes will be fine for the BF Bandmaster full wave rectifier (not a full wave bridge--- different type of rectifier)----i once replaced the stock Fender diodes in a BF Showman with 1N4007's while chasing down some noise problems---- i didn't notice any difference in the sound of the amp (the rectifier diodes weren't the problem)--- so if the stock orig diodes are good, replacing them may not offer any tonal advantage.
The 100uF/450V caps (1st filtering stage) will be fine----- these are arranged in series in this amp so they act as a 50uF/900V cap---- the stock spec 70uF/350V caps in series act as a 35uF/700V cap---So the real difference is 50uF vs. 35uF.......I'd consider this an upgrade and also since the tolerance of E-caps in general is quite broad, either one would be suitable.
I recently built a 6G6-B (Blonde Bassman) modded preamp into a 50 watt Marshall output section amp with @100uF (220uF/450V x 2 in series) total filtering on the 1st stage--- this amp sounds especially good with a Strat.
So don't worry about 35uF vs. 50uF filtering on the 1st stage---- the difference would probably be difficult to even notice................gldtp99

[r0bo01]

thanks clifton!
amp has checkered past. way back just after getting it, made smoke, etc. i shut off. friend said "i can fix it". he did. on inspection now, 2 of the 6 diodes are different (no idea what they are-1 is spherical, the other more cylindrical, but not like the remaining 4). ran this way for ~5 years.
around '78 or so, i replaced all resistors, caps (but not diodes). ran this way for years.
about 2 years or so ago, amp start making "graat graat" sounds, especially if tapped. sometimes tapping got rid, sometimes (increasingly) not. this a while after retubing pre and power and rebiasing (used euotubes biasing socket which allows plugin meas. of grid current ~42ma). reflowed solder joints. latest was replacing power tubes again.
still "graat graat".
lastly (this is bad), overcrimped pwr tube socket conns, had to push very hard to get tubes in. now, very low distorted vol. hope all i did was booger the tube(s).
have parts to recap (my replacements 20 yrs old now...), rediode even tho is probably bad solder that i missed. or, worst case ot or pt fry finally coming home.
sigh. amp sang with JJs biased as above. no redplate either.

[r0bo01]

thanks to all for your replies.
i guess time to get hands dirty. starting with seeing what kind of b+ i've got...
cheers

[Manic]

Best of luck Robo01. Yeah, sounds like You been round and round with that thing!

I LOVE My '69 Bandmaster(black faced of course) It's not as pretty sounding as alot of BF/CF(BF'd early models) Fenders I have heard. My buddy has a very similar unit to mine. His is alot prettier sounding. Mine kinda has a marshall-ish sound, but still retains some of its BF roots. Perty kool if Ya asked Me.

Let us know if You would, how it turns out?

C. Smith

[r0bo01]

that i will, clifton.

1 laaast question. do i have to "condition" the filter caps w/undervolt? or is this a lotta foo?
i have no access to variac. if need be could rig light bulb (50w? 110w?) in series w/(1)main for voltage drop. ghetto, but best i can do...

robin

[tubeswell]

Forming caps is fooey AFAICT. I just chuck new caps in and switch it on.

[Enzo]

Think about it this way. When Fender, and Marshall, and Peavey, and Mesa, and Crate, and anyone else you can think of makes an amp, they don't stop and "form" their caps. And yet tens of thousands of these amps go out into the world and work just fine. No one formed the caps in the millions of TV sets and stereos in the world, and they work just fine.

[Chuck H]

Originally Posted by Enzo

Think about it this way. When Fender, and Marshall, and Peavey, and Mesa, and Crate, and anyone else you can think of makes an amp, they don't stop and "form" their caps. And yet tens of thousands of these amps go out into the world and work just fine. No one formed the caps in the millions of TV sets and stereos in the world, and they work just fine.

I can't vouch for this myself, but...

I read that back in the day of electronic stores (the kind you actually walk into) that many MFGs of electrolytics had a shelf life associated with the different batch codes. Usually a year. And if a batch sat on the shelf too long it was up to the distributor to send them back to the MFG for either re-forming or replacement.

Point is, if this is true, all the stereos, etc. of the world were probably made with comparably fresh caps. Today most major brands of anything have components shipped direct from the MFG to the factory (probably in China). But we hobbyists still buy our parts from a warehouse most of the time. So if the shelf life info is true it's up to these warehouses to rotate stock and maintain "freshness". You know that isn't happening.

I do know for sure that buying NOS electros is a bad idea from reading posts by other experienced builders. I also know that if I build a power supply with old caps I've had around for five years it will ghost and hum like crazy.

I've never tried re-forming caps. I buy them and take my chances that they are fresh. I've only had one bad experience with what I assume, by their behavior, were old caps. But I would consider rigging up for forming new caps if I manufactured on any kind of scale. Unless I could charge the component distributor with guaranteing freshness.

Chuck

[Enzo]

The shelf life had to do with the caps chemically deteriorating. The cap makers didn;t want retailers selling spoiled product any more than a baker wants old loaves on the store shelves. The store could send back the expired product for replacement. The cap maker was not going to "service" the returned caps. They would just replace them with fresh product.

Dielectric formulations are vastly improved in the modern era.

[Chuck H]

Originally Posted by Enzo

The shelf life had to do with the caps chemically deteriorating. The cap makers didn;t want retailers selling spoiled product any more than a baker wants old loaves on the store shelves. The store could send back the expired product for replacement. The cap maker was not going to "service" the returned caps. They would just replace them with fresh product.

This I knew. Although I may not have it exactly right My understanding is that the liquid electorlyte sandwiched between the oxide aluminum layers crystalizes with age (like honey in your pantry) and that this effect is worse if the caps are unused for long periods of time. Probably because, like honey, it takes heat to re-emulsify the crystals and restore it to it's original viscous state. Heat is supposedly one element to re-forming old caps.

I guess I question this to some degree because whenever I've seen a blown power filter there is always plenty of elecrolyte goo that came out and I don't recall seeing any crystals in it. Just stinky caustic oily $h!t. Maybe it's true on a smaller scale and I just can't see the crystals.

Originally Posted by Enzo

Dielectric formulations are vastly improved in the modern era.

This I didn't know. As far as I knew it's always been the same oily stuff inside. I do know that I buy my caps when I need them, put them in and fire up my amps with no ghosting or hum issues. And I test my amps dimed because with most of them that is how they will be played much of the time.

Not to steal the thread, but I'd like to know more accurately why caps go bad and what kind of benefits new design caps have over old design caps.

Chuck

[Enzo]

The one clue is that the can cap of 50 years ago was the size of a frozen orange juice can, while the same value and voltage cap of today is the size of your pinkie finger. Materials science in general has advanced greatly in th last few decades. Even if we used the same stuff, we are nowdays better able to make things with it. Processes are as lot more consistent and precise, conditions a lot more controlled.

Here is a link to some papers on caps, specifically failure modes, and storage should be of interest. I am sure other cap makers would have similar resources, you might look around. I note they explain how to refrom e-caps, but i still don't think they would be taking them back and doing that. Labor costs a lot more than parts do.

Illinois Capacitor, Inc. - aluminum electrolytic, metalized film, igbt, power film, organic semiconductor

And this:
FaradNet Capacitor Glossary


And this:
Electrolytic capacitor - Wikipedia, the free encyclopedia

And if you still want more, google capacitor electrolytes and go nuts.

[Gtr_tech]

Originally Posted by Chuck H

I guess I question this to some degree because whenever I've seen a blown power filter there is always plenty of elecrolyte goo that came out and I don't recall seeing any crystals in it. Just stinky caustic oily $h!t. Maybe it's true on a smaller scale and I just can't see the crystals.
Chuck

Right....you won't see crystalized electrolyte because the cap was heated to the point that the electrolyte boiled and blew the seal.

I always check the condition of new caps just so I don't have a dud get through. I don't need any bad press 'cause a marginal cap caused a guy's newly rebuilt amp to blow smoke within a few days. It doesn't make the cap mfgr look bad, it makes *me* look bad if this happens.

[r0bo01]

well, once i started digging, under the doghouse cover found one of the 20uf caps had a mound 'o schmutz on its endplate. now am committed 'cause firing up to poke around probably wouldn't be good idea...
so, replace all the caps w/those in the kit (100uf x 2, 20uf x3, 25uf x 5) as well as the rectifier diodes. find a few suspect connections/solder joints, fix. fire up, check b+ @ + end of caps and stdby switch - 444v +-1 or so. let run w/o pwr tubes (on stdby) for 1/2 hr as nod to filter caps. check grid bias - 42ma and...
happy days! she's a worka! seems more power than before and better tone.
then, about 15 min into session notice low level squealy oscillation rising and falling. oh crap. shut down discouraged. next day, take apart and poke around looking for obvious problems, none. put back together and fire up.
worked fine. played thru a practice set am working on. sounds fine.
could it be caps had to "settle in" somehow? in particular, the 25uf 25v caps from kit that go to ground in para w/resistor from each cathode of preamp & vib tubes?
kit also had 100uf 100v electrolytic i couldn't find on board or in schem. used in older bandmaster?
anyway, thanks again to all for help/encouragement (and putting a fire under my tail).

[Dave Curtis, dB AudioTech]

"kit also had 100uf 100v electrolytic i couldn't find on board or in schem. used in older bandmaster?"

That's for the bias supply.

[r0bo01]

That's for the bias supply.

the higher values ok? mine's 25uf @ 50v. resistors (15k, 10k l-pot, 470 1w) handle it?
while about it, can i use one of my 1n4007 to replace the diode there?

thnx again.

[MWJB]

Use a 100v cap ("+" to ground), rather than 25 or 50v. You might see -60vdc+ when all biased up with some brands of power tube.

Yes a 1n4007 will be fine in the bias supply, remember stripe goes to the PT.

[Dave Curtis, dB AudioTech]

Originally Posted by r0bo01

the higher values ok? mine's 25uf @ 50v. resistors (15k, 10k l-pot, 470 1w) handle it?

Yes, 100uF is going to stiffen up the bias supply (you really don't want a squishy bias supply). On some other amps (without a separate bias tap on the PT), it would be too much, but not on the Bandmaster. If you're worried about it, test and see how long it takes the bias voltage to charge the cap. I have a 220uF in this spot in my Pro Reverb.

Originally Posted by r0bo01

while about it, can i use one of my 1n4007 to replace the diode there??

Yes, remember this is a negative supply, so the cap and diode are installed "backwards" (positive and anode to ground).

[r0bo01]

Originally Posted by Dave Curtis, dB AudioTech

Yes, 100uF is going to stiffen up the bias supply (you really don't want a squishy bias supply). On some other amps (without a separate bias tap on the PT), it would be too much, but not on the Bandmaster. If you're worried about it, test and see how long it takes the bias voltage to charge the cap. I have a 220uF in this spot in my Pro Reverb.

Yes, remember this is a negative supply, so the cap and diode are installed "backwards" (positive and anode to ground).

k. i was afraid of somehow zitting the 470 1w resistor as 100uf charged up. in retrospect, silly, so will prolly go for it this wknd.

thnx for your reply and everyone's, am learning something new every day here! (& i got a lot to learn...)