Fender Hot Rod Deluxe Died Suddenly

[tmlesko]

I had this amp on for a while last night, it suddenly quit all together - no sounds, no smoke, just a slight smell. The fuse is good, the jewel light does not illuminate. I just printed the schematic, however, it is small and hard to read. I plan on giving it a good visual inspection and begin to troubleshoot. I was an electronics tech. 40 years ago, however, I forgot most of what I knew. I believe I remember enough so I won't hurt myself I have a good meter, rubber mat and an isolation transformer but no variac.

I have not found a guide to troubleshooting one of these or any procedures so I will start at the power supply and work from there. I do have Justin Holton's website info. Any help/guidance would be greatly appreciated!!!

Tom L.

[Chuck H]

You say there was a "smell" and the pilot doesn't come on, but the fuse isn't blown. Hmmmm... It sounds like the PT filament winding or some associated component went poo. If this is the case I'd guess a tube is responsible and repairing the amp without replacing the offending tube would result in another failure.

[tmlesko]

Thanks Chuck. Well, I didn't have to look very hard/far, there is no voltage coming out of the PT as you suspected. Everything on the input side of the PT seems fine. I do not have a 'working' tube tester at the moment but may be able to borrow one soon. Would you suspect one of the power output tubes? I found a replacement PT for $58 + shipping from Triode Electronics, USA made. http://store.triodestore.com/hotroddeblde.html I do have the original tubes that I replaced a short time ago, all were working, I can certainly use them until I can test the ones in there. Any other thoughts?

Thanks,
Tom L.

[Chuck H]

there is no voltage coming out of the PT... Any other thoughts?

If there is NO voltage from the PT secondaries I would think there is a fault in the PT primary. So there is a good chance that there are no problems with the tubes. My initial thought was that there may have been a short in one of the tubes that caused a fault in the filament circuit, in which case you would see voltage on the HV and lowV PT secondaries but none on the filament secondary or a fault in the filament circuit. That's because I've never seen a spontaneous primary PT failure. But with no secondary voltages anywhere I'd have to think that you have an open PT primary wind. I didn't suspect it first because I have never seen this happen. But hey, these are relatively inexpensive, mass produced amps so who knows what can happen. With no PT secondary voltages I would guess that the tubes are OK and this is an acute failure. But do test the tubes anyway if you get the chance.

[tmlesko]

Thanks again Chuck,
I haven't had a chance to get back to it, but just to be sure, I will check the primary for continuity. Let you know!

Tom L.

[Jazz P Bass]

On the primary side is a current limiting NTC resistor.
Check this item for an open condition and/ or bad solder connections.

[tmlesko]

Yes, thanks Jazz P, I did check that (thermistor?) the other day, which is fine. I just got some time to have another look at this and just checked the primary winding of the power transformer, which is definitely open. Most likely I will just replace it. Antique Electronics Supply has the replacement Fender PT, might have a look inside this one for curiosity sake, maybe I can repair it. I am not that cheap, just curious to see if I can.

Thanks again to both of you for your help, I am curious if you have any other thoughts, I appreciate the "re-education!". I am enjoying this again actually, I was trained by the Air Force on tube electronics and solid state as well, in the late '60's when they were using both in aircraft. I repaired mostly tube equip. back then because it failed more often than the newer stuff, but it has been 38 years since I was in that field and I have forgotten so much!

Happy New Year!
Tom L.

[Chuck H]

The last time I played in a band was about fifteen years ago. We were together a long time and had eight ten song sets we would rotate. I can't remember even one song all the way through and have completely forgotten most of them.

This is a great place to learn and ask questions. I'm basically a hack mod guy without a clue that grew into a designer here over the last sixteen or seventeen years.

It's funny how many other forums posters (amp garage, gear page, etc) credit this site as the place where they "started" before graduating to better more progressive places. Like we're a bunch of stodgy farts here. It figures because anyone who starts here and leaves didn't "get it". It's also why this is the most tech savy forum of it's kind, and I say that with no pretense of humility although I wouldn't include myself among the better tech contributors here. We don't really specialize in one kind of amp and we don't go in for NOS filter caps, carbon comp resistors, thirty dollar film caps and cloth braded wire. Far from stodgy or not progressive, we get to the brass tacks of how to make new ideas (or individualy newly discovered ones) into reality.

That's my sales pitch for Ampage.

[tmlesko]

Thanks Chuck,
I don't know what "Ampage" is. . . one of the members? Anyway, back on topic, I will post my results with the transformer repair soon. I joined this group a couple years ago when I got this amp and the reverb didn't work, members were very helpful. I only have 2 amps and don't 'play' guitar. . . I just play "at it" and try to play slow, old jazz. . . (like Joe Pass on sedatives,) I can't even manage that but I try anyway. I got an N.O.S. EICO 666 tube tester 'kit' a while ago "never been assembled (!) " with some parts missing that I have since gotten, looking forward to putting that together, although a friend suggested that I leave it as is and get another one to use. My first amp back in '69 was a Bogen all tube PA amp that I converted for guitar and melted several cords on those exposed tubes. I guess I fit the bill as a stodgy old fart too.

Tom L.

[Jazz P Bass]

Power Transformer primary windings may have a fuseable link embedded in the winding wrap.
Betcha that is what went open on you.
Which begs the question: why did it fail.

[tmlesko]

Indeed. . . voltage spike? Perhaps the really, really, REALLY bad music I play???

Tom L.

[Chuck H]

Tom, Ampage is here. As in 'where you are now'. This is the forum that comes up in the search engine if you type in Ampage and that's the forum name on the home page.

[tmlesko]

Power Transformer primary windings may have a fuseable link embedded in the winding wrap.
Betcha that is what went open on you.
Which begs the question: why did it fail.

Yes indeed, why did it fail? Well, I finally got back to the amp, looked into the primary windings as suggested, couldn't see anything resembling a fuseable link, just wrapped windings. I bought a Fender direct replacement transformer from Antique Elec. Supply, had the amp on for about 20 min and . . . I am afraid I just fried another PT! The only component on the primary side is that thermistor but it is not open. Can the thermistor be failing in another way causing additional current to flow through the primary windings and causing an open in the winding??? Doesn't seem right. if not, is there anything on the secondary side that can cause a primary winding to open? It seems improbable that two Fender transformers were bad/at fault. At this point, I don't know how to test anything else without a working transformer except the tubes . . .Any suggestions???

Tom L.
Hot_Rod_Deluxe_schematic 2 pages.pdf

[Chuck H]

Are you testing the primary wind at it's own leads or through anything else? Really tough one. I've got nothing. If the thermistor is conducting thats fine. If it's not that's fine too but the amp won't turn on. Nothing about it should blow the primary open. I suppose if the primary is wound with insulation really close to spec that a kick back voltage from the secondary could open the primary. But that would seem really odd to me.

[tmlesko]

Yes, I am testing at the primary leads. What are the chances that the new transformer, and the old one, was defective in manufacture, since they both were Fender components? Slim, I know, and I doubt that Antique Electronic Supply, where I bought the replacement, will give me another one, I will try though. Otherwise I will find another brand locally. Since it took about 20 min. of operation for the winding to open, I can check test point voltages with another new one in the circuit and if all is normal. . .

Tom L.