The Steel Guitar Forum

My BF Tremolux started losing power, distorting, and blowing fuses.. It was totally electronically restored by Tracy Sands, and he has an excellent reputation.. Anyway, I pulled the power tubes and rectifier out, powered it up, and it idled for hours, no problem... Put the power tubes back in, still idles for hours no problem.. The rectifier is a Chinese built Rubytubes 5AR4... I have heard that the MIC 5AR4 tubes had a failure rate approaching 50%.. Just something I read online...

So now that is does not blow fuses and all tubes except the rectifier are in and the amp is on, NOT on standby, should I assume it was a bad 5AR4, replace it, and see what happens??... Any other advice???... bob

Well, you could try it...but if the rectifier is not in, then you aren't supplying the power tubes with B+ so they aren't really working at all.

Don't be surprised if something else is still wrong, but if the rectum-friers have that bad a reputation, that's what I would try first!

Mike

Easiest check is replace rectifier, then check B+ voltages. If it still blows fuse, a shorted tube, capacitor or OT COULD be problem. Remove all tubes except 5AR4. If it still blows fuse, I suspect a shorted filter cap although it could be something else.

I always add 2 diodes in series with pin 4 and 6 of the rectifier tube - that way if the tube shorts, the diodes protect the expensive power transformer. You can add a terminal strip to the socket lug and run them right to the socket.

also, if the tube shorts in the middle of you using the amp, the amp will still work (it will get a bit louder and gritty because of higher B+)

if the tube opens up, the amp will die but still have a power light on

found a picture

I use 6A 1000V diodes

Looks like a 1N4007, 1 amp diode at 1000 PIV. I have 6 amp diodes in the shop, they are a lot bigger around than that.

good eye! The picture is from one of my low power amps. It is more of a general reference of how to do it.

on the big amps, I use the big guns and yeah, they are a little thicker. The leads on the 6A diodes are really something to contend with!

That is a good idea, Tim. I have seen it before on a website for recommended mods for tube amps.

Yea, those 6 amp diodes are some honkers for sure. I like to also use a CL-60 (current limiting thermistor) in series with the hot side to the AC fuse to help slow in-rush current. I did that on the amps I was building. I also fused the 5 VAC and 6.3 VAC supplies as well.

well anyway, Put all tubes back in, ran it for hours and hours.. Been playing it on and off last 2 days.. No issues.. Who knows????.... bob

check the rec tube pins, I've seen many where the solder breaks in the pin, and just resolder it
.

When I first acquired my 64 Tremolux, it blew fuses as well , it was indeed caps on the RECT side of the stand by switch...16 ufd's...the rectifier socket was also suspect but not the problem, the caps were. The good news was that the caps did not take out the GZ34.


In this case I would revisit the rect tube and socket.

I would let it sit with the Rect tube installed and the power tubes OUT...the reverse of what you did...monitor the B+

or not !

I really like Tim's photo above, great recommendation....

I agree, Tony. I would monitor the temp on those 16uf caps. If they have a high ESR, they will be getting warm. If so, replace them. Also if the bias was set too hot then the amp may be going into "red-plating) on the power tubes. Looks for red spots on the plates of the power tubes. If you see them it is biased too hot and can go into full red-plating, which will blow a fuse quickly.

Never red plated.. Tubes NEVER ran hot... At this point, it no longer blows fuses, and I have no idea why it did in the first place.. I did run run the amp with no power tubes and rectifier in for hours, and power tubes in rectifier out for hours,, never once at any time I have had this amp did the power tubes get anywhere near hot.. Its been days.. i play it every day, and its been fine... I have no idea what happened... bob

Bob , the amp is broken and cannot be repaired, please send it to me I will dispose of it for you !

Are you using slo-blo fuses? Heating up the filter caps may have re-formed them... Or you might have a carbon trail across some tube pins that you disturbed when you pulled the tubes (doubtful). If this is a gigging amp I'd have it thoroughly gone over.