converting to solid state rectifier

[pontiacpete]

I built a bassman 20 recently with the power supply from the deluxe reverb ab763 circuit using a deluxe trafo and the bias supply set up with the adjustable pot and a standby switch. I'd like to change out the tube rectifier(gz34) and put in a bridge rectifier but I'd like to keep the adjustable bias supply. I'm having a problem figuring out the wiring. I've tried clip leading it in on a breadboard and haven't had any luck.
Is there anyone here that could help be with this?
thanks in advance.
pete

[black_labb]

a bridge rectifier could make the bias a bit difficult to put in. i'd suggest using a full wave rectifier. its the same type of rectifier as the tube rectifier, just using diodes as opposed to the tube. bridge rectifiers are suited to when you have a single winding, not a center tapped winding like you would on an amp with a tube rectifier.

otherwise there is no harm. you can upsize the first filter cap if you want to get an even tighter sound, and maybe less hum if the amp has much b+ ripple.

[pontiacpete]

not sure how to work this forum, I ended up replying with the 'quick' reply.
Anyway, the full wave rectifier seems to work well.
thanks.
I now have a static like hum like a grounding issue happening. Since the PT is from a deluxe there are the 2 yellow wires still attached to the octal socket with 5vac across them. Could this be the source of the noise?
If so, do I ground one of them? They seem to be tapped to the winding that goes off to the bias supply circuit as in the deluxe rev which in this case is the blue/red wire.
thanks for the help.
pete

[Chuck H]

DO NOT GROUND THE YELLOW WIRES!

PT death will ensue.

If all else is the same besides the rectifier, and the amp was quiet before, you may have a mistake in your bias supply wiring after tinkering.

Chuck

[pontiacpete]

Thanks, Chuck

[pontiacpete]

I actually was able to set the bias to the specs of the bassman 20 schematic, -33vdc.
Maybe I should connect the 2 yellow wires?

[pontiacpete]

That didn't work! I tried clip leading the two yellow wires and fried my clip lead.
What to do?

[pdf64]

Try waiting for an answer before you short out a winding!
I'm worried that you know just enough to be dangerous. No one here can know if you've grounded you chassis properly etc, and you are risking a major transformer failure which could make the chassis live.
Read up as much as possible on stuff you're thinking of doing,
aikenamps.com
geofex.com
Then ask questions here before you go ahead.
You need to get an understanding of why what you've done just was a bad idea.
Re bias, you need to understand why setting the bias to the specified -33V is entirely the wrong way to check it when you moved from a tube to a silicon rectifier. Peter.

[Jag]

+1

You really CAN kill yourself with this stuff.

[pontiacpete]

Dumb move on my part. I'm usually more cautious. I have it plugged into an outlet with a 100W bulb as a limiter and forgot that the limit switch was not on when of course it should have been.
No apparent harm done to the PT. It's still powering up with the loud hum.

Do I need a dropping resistor on the cathodes of the two IN4007s?
Any suggestions would help.

thanks all

[pontiacpete]

I put a 470 ohm 2W resistor on the anodes of the 2 diodes and connected the other end of the resistor to the standby switch.
This seems to have reduced the hum, maybe in half, but I still have it.
I'm thinking that maybe a higher resistor might do. No?

[pdf64]

Please stop dicking around with this.
Put it back how it was.
Learn electronics on some low voltage stuff, like effect pedals.
This is like a commentary from someone who has a blindfold on as he walks along a cliff edge. Peter.

[pontiacpete]

Thank you Peter

Point well taken. I am a newbie at electronics. I have built about 10 working effects pedals for myself. It was a great learning process. I put together a kit and built two clone amps from skratch. Gerald Webers kit, the newjoyzee, a blackface deluxe and super reverb. More great learning for me and all of them work great and have proven so for a couple of years, which included many professional gigs.
I've been doing a lot of reading and have a mentor, an electrical engineer guy helping me with theory stuff and the mathematics behind it. We worked through a number of repairs on transistor amps , i.e. GK400 , polytone brute bassamp, heathkit IP 17 some antique radios and my Scott Stereo etc, etc.
This particular thread I started is of a build I made funded by a fellow musician i.e. he paid for the parts I did the labor with the hope learning more. It was made about a half a year go and has worked fine for several gigs and rehearsals for him. He wanted a small tube amp for such.
Anyway, here's where the problem of this thread starts. I never diverged from a schametic/layout of any of the my builds so far, but on this one I tried using a deluxe PT for a bassman 20 with a tube rectifier. It that has been working. Well, my friend loves the sound but, of course, he wants it a bit louder. So I decided to put a solid state rectifier in(years ago Harry Kolbe did it for me on a 70's princeton, which I since reversed) with the thought that it might give him a bit more power. Is this true in your opinion? Nonetheless, I never have done a conversion to a SS rectifier whatsoever, and hope to learn how. Do you have any advice that would help other than trying to discourage me?
BTW, there's a really great forum that started reading about 6 months ago called Funwithtubes run by Max Robinson, a retired EE professor.
They always say to the new guys that there are no stupid questions, I hope this forum is like that too.

Best Regards,
pete

[JoeM]

Originally Posted by pontiacpete

I never diverged from a schametic/layout of any of the my builds so far, but on this one I tried using a deluxe PT for a bassman 20 with a tube rectifier. It that has been working. Well, my friend loves the sound but, of course, he wants it a bit louder. So I decided to put a solid state rectifier in(years ago Harry Kolbe did it for me on a 70's princeton, which I since reversed) with the thought that it might give him a bit more power.

Best Regards,
pete

Why not just get one of the SS modules that plugs in the tube rectifier socket? Then you can go back and forth with a tube rectifier (with a re-bias), without having to do any permanent mods to the amp.

[pontiacpete]

joe
Thanks. I did a search for this but haven't come up with anything. Can you send me a link?
At this point the hum problem is solved. I added 2 more diodes in series each on the primary, and the AC hum is practically gone, but I would like to have one on these plug in SS rectifiers to try on other amps.
pete

[Regis]

I pinged Old Tele Man (Earles) a while back about this, here is his reply and a pic. You can get sockets from Doug Hoffman or I suppose you could bust up an old tube. I thought I had info on adding resistors for sag but can't find it. It might have been in one of KOC's books.

1) solder anode-end of one 1N5408 diode (or equivalent) to pin 4 of octal socket.
2) solder anode-end of other 1N5408 diode to pin 6 of octal socket.
3) solder the two cathode-ends of of the 1N5408 diodes together into pin 8 of octal socket.

The 1N5408 is a hefty high-voltage diode; but, you could use cheaper 1N4000-series diodes, but will have to "stack" three of them in series to handle the high voltage, just to be safe.

[Steve A.]

Another alternative is a simple switch to go between a solid state and a tube rectifier:

http://www.blueguitar.org/new/schem/...ct_ss-tube.gif

And yes it does throw the bias off a little so you look for a setting that will work with both positions of the switch.

Steve Ahola

[JoeM]

I've used the base of tube that died for this too, but you can get the SS module type.

Weber has a Copper Cap version with just the diodes.

http://www.webervst.com/ccap.html

(Scroll down the page for the WS1)

[pontiacpete]

Joe, what did you use for a cover when you converted the dead tube to a SS rectifier?
I finally ended up using 3 diodes(IN4007) in series on both of the secondary lines.
To protect the diodes I put .0022uf caps and 1 meg resistors in parallel on each. Then I added in the hum pot that the bassman 20 has in the schematic and no more AC hum.

Thanks to everyone for the links and the help!

[JoeM]

Originally Posted by pontiacpete

Joe, what did you use for a cover when you converted the dead tube to a SS rectifier?
I finally ended up using 3 diodes(IN4007) in series on both of the secondary lines.
To protect the diodes I put .0022uf caps and 1 meg resistors in parallel on each. Then I added in the hum pot that the bassman 20 has in the schematic and no more AC hum.

Thanks to everyone for the links and the help!

I cut a piece of perfboard and used epoxy to attach it.

[bluemonk]

QUOTED:
1) solder anode-end of one 1N5408 diode (or equivalent) to pin 4 of octal socket.
2) solder anode-end of other 1N5408 diode to pin 6 of octal socket.
3) solder the two cathode-ends of of the 1N5408 diodes together into pin 8 of octal socket.
The 1N5408 is a hefty high-voltage diode; but, you could use cheaper 1N4000-series diodes, but will have to "stack" three of them in series to handle the high voltage, just to be safe.
END QUOTED

it seems that 1N5408 are not higher voltage than 1N4007 but have higher current handling (3A).
Is it safe to use just one 1N5408? Or should they be stacked just like 1N4007?
Thanks

[Albert Kreuzer]

The diodes should be able to take at least double the plate voltage. As long as B+ is less than 500V, one 1N4007 per side should be sufficient. Two is better, three is plenty.

Cheers,
Albert

[socalscott]

Weber has the plug-in mentioned, but it may mimic a tube.

Any reason you didn't use the advice to stiffen things up with a cap?

[pontiacpete]

this amp, a clone of a fender bassman 20, was designed with a solid state rectifier. I thought I would try a tube rectified and there was too much sag and not enough volume for a bass so I converted back to a silicone diode rectifier. I think I used 6 diodes all together, if I'm remembering correctly, and I backed those up w/ caps and resistors in parallel. I think that amp will be coming back to me, because of an intermittent problem, cutting out, I'll be able to look at what I did.