sonolink

Help finding correct component with Fender Hot Rod Deluxe
« on: January 12, 2019, 06:36:22 AM »
Hello everybody

The other day a friend came by with his fried Hot Rod Deluxe. While he was gigging the amp began smelling like burnt and stopped working. Back at home he replaced the fuse but it was blown as soon as he switched the amp back on. So he called me and I told him to replace the fuse, take out the tubes and flip it on. The fuse held. So he replaced all the tubes.
When he switched the amp on the sound was low output and distorted. So I told him to bring it over. After inspecting visually the amp I saw that at least one diode was burnt. I think it's called a flyback diode. The thing is, I don't know what a "flyback" diode is (could someone please explain) and I assume that although marked C5 on the PCB, it should be CR5 on the schematic. I also assume it's a protection diode and after a quick search I think the correct value is 3000V/0.25A.

My questions are:
-Can this diode be replaced by another one like 4004 or 4001? I'm asking cos I got a bunch of those that I use as rectifiers for amps
-Should I check other components that could have been damaged aswell (apart from the obvious resistor next to the diode of course) and if so, any suggestions?

https://imgur.com/a/QC5JS9K
https://imgur.com/a/2ugQNkU

Thanks a lot for your help :)
Cheers
Sono
Why sleep when you can mix?
M.P.Stavrou


Mylithra

Re: Help finding correct component with Fender Hot Rod Deluxe
« Reply #1 on: January 12, 2019, 07:19:19 AM »
All they have in the service manual is that those parts should be 3kv at 200ma:

qty    P/N                      Desc.                                             Designation
2         029690001   DIODE HV 3KV 200mA    CR4,5

http://www.tangible-technology.com/schematics/fender/hrd/Hot%20Rod%20Deluxe.pdf

sonolink

Re: Help finding correct component with Fender Hot Rod Deluxe
« Reply #2 on: January 12, 2019, 07:23:12 AM »
Thanks for your fast reply Mylithra :)

Any other parts that maybe I should check?

Thanks
Sono
Why sleep when you can mix?
M.P.Stavrou

Walrus

Kevin.

sonolink

Re: Help finding correct component with Fender Hot Rod Deluxe
« Reply #4 on: January 12, 2019, 07:54:22 AM »
Excellent!
Thanks Kevin, and thanks for the link too ;)

Cheers
Sono
Why sleep when you can mix?
M.P.Stavrou

squarewave

Re: Help finding correct component with Fender Hot Rod Deluxe
« Reply #5 on: January 12, 2019, 10:44:13 AM »
That's just a high voltage power rectifier diode. Presumably it's protecting the tube from some sort of inductive kick from the OT. There's no signal going through that of course. It's not obvious to me what the the voltage rating should be but if you have a 1N4007 (and probably lower) that would work fine. There's no reason to think that there's anything wrong with those resistors (unless the one got blow-torched by the diode when it went maybe).

sonolink

Re: Help finding correct component with Fender Hot Rod Deluxe
« Reply #6 on: January 12, 2019, 11:07:43 AM »
Thanks for your reply SquareWave. I think that my friend had very old tubes on the amp and that one of them finally shorted or whatever and that blowed the diode and the fuse.
Am I right?

Cheers
Sono
Why sleep when you can mix?
M.P.Stavrou

squarewave

Re: Help finding correct component with Fender Hot Rod Deluxe
« Reply #7 on: January 12, 2019, 11:34:48 AM »
Thanks for your reply SquareWave. I think that my friend had very old tubes on the amp and that one of them finally shorted or whatever and that blowed the diode and the fuse.
No. Diodes don't burn out like that. Diodes are usually pretty indestructible. It was probably defective from the beginning. It failed short and that blowed the fuse (and hopefully saved the OT in the process).

Just make sure that do a good job soldering in the replacement. Try to clean off any soot around the pads and use flux if you have it.

JohnRoberts

Re: Help finding correct component with Fender Hot Rod Deluxe
« Reply #8 on: January 12, 2019, 11:51:19 AM »
No. Diodes don't burn out like that. Diodes are usually pretty indestructible. It was probably defective from the beginning. It failed short and that blowed the fuse (and hopefully saved the OT in the process).

Just make sure that do a good job soldering in the replacement. Try to clean off any soot around the pads and use flux if you have it.
Diodes can fail from reverse over voltage, and forward over current (the silicon literally melts and becomes a short circuit). When a fuse is involved, one would expect the fuse to protect against over current.

JR
John Roberts
http://circularscience.com
Tune it, or don't play it...

sonolink

Re: Help finding correct component with Fender Hot Rod Deluxe
« Reply #9 on: January 12, 2019, 11:54:44 AM »
So the reason of the failure wasn't the tube? The tubes were pretty old according to him and the diode was in there from the beginning...

What do you reckon was the cause then, an old tube or a defective diode?

Cheers
Sono
Why sleep when you can mix?
M.P.Stavrou


moamps

Re: Help finding correct component with Fender Hot Rod Deluxe
« Reply #10 on: January 12, 2019, 12:26:18 PM »
So the reason of the failure wasn't the tube? The tubes were pretty old according to him and the diode was in there from the beginning...

Most probably it is (too high power and current of G2 when the amp is in overload, for example).
Have you really checked the diode with DMM? Maybe it is just dirty from the holy smoke of the closest burnt resistor?

pucho812

Re: Help finding correct component with Fender Hot Rod Deluxe
« Reply #11 on: January 12, 2019, 12:41:10 PM »
Low output and distorted, is psu working properly?
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

moamps

Re: Help finding correct component with Fender Hot Rod Deluxe
« Reply #12 on: January 12, 2019, 12:48:47 PM »
Low output and distorted, is psu working properly?
One burnt G2 resistor means a significant DC current dis-balance in primary of PP transformer what can be the cause of low and distorted signal.

sonolink

Re: Help finding correct component with Fender Hot Rod Deluxe
« Reply #13 on: January 12, 2019, 12:56:05 PM »
Most probably it is (too high power and current of G2 when the amp is in overload, for example).
Have you really checked the diode with DMM? Maybe it is just dirty from the holy smoke of the closest burnt resistor?

Thanks for the input moamps! I just finished cleaning the PCB and guess what? The diode space is pristine clean whereas the resistor's is burnt bad!!  (actually the resistor broke in pieces when trying to pick it out)
https://imgur.com/HAbytVP

So I cleaned the diode and I think it's just as you say, dirty from the smoke of the fried resistor :)
I tested the diode with my DMM and I get 1.74v when putting the black terminal on the cathode (and the red on the anode), and OL when swapping them around. I think it's working fine and got dirty by the resistor that was overloaded by an old tube that shorted or whatever.
Makes sense?

Low output and distorted, is psu working properly?
I think it was before the problem. I think the source of the problem was an old tube. I could be wrong though
Why sleep when you can mix?
M.P.Stavrou

Mylithra

Re: Help finding correct component with Fender Hot Rod Deluxe
« Reply #14 on: January 12, 2019, 01:59:49 PM »
The diode Id consider replacing just in case it got physically damaged when the resistor went. If that is the screen resistor right next to it that blew up, I consider those fairly high wear parts in a tube amp. It probably was an output tube that went up in smoke and took the screen resistor with it. Not all that uncommon when an output tube fails.

Id replace the screen resistors, probably the first stage power resistor, that diode then do a power on check.

After replacing the fried parts.
CAREFULLY check voltages. There's 350+v in there. With no tubes in, the voltages across the different sections will be high and not all that different since there is no current being drawn.

Pin5 of the output tubes is the grid. You should see some Negative voltage there. What does this read. If there is no voltage there, then the bias supply is the problem.

If the amp has a preamp out, with only pretubes in it, do you get a signal at the preamp out and in turn at pin 5 of the power tubes?

Most of the tube amps I've looked at had fried power amp sections. Rarely preamp problems. The problems most often manifested in tube that went into runaway, drew too much current for adjoining parts and blew them up. What caused the tube to go into runaway is the question.
« Last Edit: January 12, 2019, 02:03:01 PM by Mylithra »

sonolink

Re: Help finding correct component with Fender Hot Rod Deluxe
« Reply #15 on: January 12, 2019, 05:43:44 PM »
Id replace the screen resistors, probably the first stage power resistor, that diode then do a power on check.

Could you tell me which one would be the first stage power resistor please?
I think this is the correct schematic:
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-Hot-Rod-Deluxe-Schematic.pdf&ved=2ahUKEwjM5e-spenfAhUsAWMBHRnzDE0QFjAAegQIBBAB&usg=AOvVaw2UcxGeG2Ow_B0A7uONCQsD

What caused the tube to go into runaway is the question.

Honestly I think it failed cos it was very old. My friend never replaced them since buying it second hand 2 years ago and God knows if the previous owner would have changed them at all...

Cheers
Sono
Why sleep when you can mix?
M.P.Stavrou

Mylithra

Re: Help finding correct component with Fender Hot Rod Deluxe
« Reply #16 on: January 12, 2019, 06:53:00 PM »
Looking at the schematic you posted, in your amp, the first stage resistor is actually the large inductor. I wouldn't suspect that to be faulty.  I wouldnt suspect any of the other power resistors to be problematic.

R62 is indeed the screen resistor.  D4 and D5 on the board are CR4 and 5 on the schematic.  Factory part for D4 and 5 are R3000 diodes. (3kv .25A rated) TubeDepot carries them.  The screen resistors on your amp are listed as 1w parts. In amps I build, these are 5w parts. I'd replace both of them. (R61, R62)

sonolink

Re: Help finding correct component with Fender Hot Rod Deluxe
« Reply #17 on: January 12, 2019, 07:05:27 PM »
Looking at the schematic you posted, in your amp, the first stage resistor is actually the large inductor. I wouldn't suspect that to be faulty.
Excellent! :)

Factory part for D4 and 5 are R3000 diodes. (3kv .25A rated)
Yes. I've already ordered them from Mouser.

The screen resistors on your amp are listed as 1w parts. In amps I build, these are 5w parts. I'd replace both of them. (R61, R62)
I was thinking 3W but I'll follow your suggestion and order 5W resistors :)

I'll report back when I've replaced those components.

Thanks again to all for your input and to Mylithra for taking the time to take a look at the schematic and helping me out with this. ;)

Cheers
Sono
Why sleep when you can mix?
M.P.Stavrou

CJ

Re: Help finding correct component with Fender Hot Rod Deluxe
« Reply #18 on: January 12, 2019, 10:07:52 PM »
those flyback doodads are protection on the speaker side, a speaker cuts loose, or some joker unplugs your speakers during break,  or you mistakenly plug the speaker jack into the foot pedal jack which should not be located anywhere near the spk jack,  what were they thinkin?


check the pwr tubes of course and check the speaker, low output/distortion could mean it is partially cooked,   how many speakers? what size?

If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

sonolink

Re: Help finding correct component with Fender Hot Rod Deluxe
« Reply #19 on: January 13, 2019, 05:47:26 AM »
could mean it is partially cooked,   how many speakers? what size?

Really?? Not that I doubt your word or experience, but I've never ever seen a speaker cooked by an old power tube failureTBH...that would NOT be cool at all :(

It's a 1x 12" speaker

You got me worried now while I'm waiting for the components to arrive....

Cheers
Sono
Why sleep when you can mix?
M.P.Stavrou


 

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