Fender Hot Rod Deluxe, Output trans. bad?

[Appaloosa]

I recently got a hot rod dlx. The previous owner said it just kept blowing fuses. the first thing I did was pull out all of the tubes, and put a new fuse in. the amp didn't blow the fuse but made loud distortion from the speaker and I could smell burning. So I quickly shut it down. On further inspection I noticed that C40 and C41 were loose on the preamp board, and leads were broken off right at the cap. so I replaced the caps, and fired it back up, but it did the same thing. I noticed the smell and light smoke seemed to come from the output tranny, (not 100% certain cause amp was still in cab.)

Whats the best way to test an output tranny? should I check for other parts that may also be bad? would these broken caps cause an output tranny to fail?

I did notice some rust on the output and power trans. stacks as well. this amp has a B-050438 output transformer in it.

thanks for any help!

[52 Bill]

Whats the best way to test an output tranny? should I check for other parts that may also be bad? would these broken caps cause an output tranny to fail?

If the OT is bad and smoking, I'd assume that it is shorting out in some manner. Read the resistance from each of the primary leads to see if there is any continuity to either the secondary or the metal frame/ground. Also compare the resistances of each half of the primary.

Did you check the other filter caps as well as the two that had broken leads?

[Enzo]

Look on the tube socket board, right next to where the brown and blue wires plug on. There are a couple diodes, CR4 and CR5. Is either one shorted? If so, disconnect them both and see if the amp works.

[Appaloosa]

thanks I will try that now and get back to you guys. Whats the best way to check the other filter caps? I don't have a capacitance meter, only a fluke 77 DMM, can I use that?

I really appreciate the help!

[Appaloosa]

I tested the resistance of the OT.
the secondary was about 1 ohm between all three wires, black-green-and green with stripe.

I found continuity from the primary to secondary.
Red to any of the secondary wires: 60 ohm
Brown to " :30 ohm
Blue to " : 170 ohm.

Between the primary wires I got:
Blue to brown: 160ohm
Red to blue: 106 ohm
Red to Brown: 55 ohm

I removed one lead of both CR4 and CR5 and tested them with diode mode on my DMM. I got no continuity on either of them . I left them unhooked and turned the amp back on with no tubes in it and the OT started to smoke immediately again, with distortion out the speaker. -same as before.

Should I now replace the OT and those DIods? What do those diodes do?

thanks again for the help.

[Jazz P Bass]

The transformer is TOAST.
The real obvious hint (other than the smoke) is the continuity from primary to secondary.
The diodes should also be replaced.
Fender spec's an R3000 diode. (25A/ 3000V)
They are refered to as 'Flyback Diodes'
RG & Ronsonic (MEF members) explain it very well here:Could somebody please explain to me how this works? (Tube amplifier content)
Google :'flyback diodes & output tubes'

[Appaloosa]

So I just got my new transformer and a pair of R3000 diodes. I installed them. I turned on the amp and for about 30 seconds it sounded great/normal. Then suddenly the volume output dropped significantly and the tone was distorted on the clean chanel. The amp does not hum. I then put a different set of tubes in it, but it still did the same thing.

Any sugestions as to what to look for? or a starting point.

I recorded the voltages of the tubes, do these seem out of the ordinary. (see attachment)

thanks very much

[52 Bill]

Did you set the bias after you installed the new transformer. etc.?

Did you check to see if there were any cold solder connections on the tube pc board?

Did you check the extension speaker jack switching contact?

Try plugging your guitar into the power amp in jack and see if the signal is clean or dirty.

[Enzo]

Go back inside, look CLOSELY at the power tube socket pins, any solder cracks? Or just resolder all of them regardless.

And next door is the phase inverter tube. Check for B+ on both pins 1 and 6.

[MikeH]

+1 on checking the power tube socket joints.

The tube socket boards on these amp are prone to problems. It's generally the first thing I check when I get one. Wiggle the socket gently while looking at the joints. They should not move. Reflowing the joints sometimes works, but often the pads are broken away from the board - check for that. If they are broken away you have to scrape off the pcb insulation on the traces and solder some small pieces of wire from the socket pins directly onto the traces. It can be tedious, but if any are broken away, you might as well do all of them.