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Old 18th October 2006, 12:03 AM   #1
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Default HOT ROD DELUXE: CRACKLE...POP...what to do?

i've had a fender hot rod deluxe for...wow...its getting close to a decade now. i had no problems with it for the first half of it's life. then i started getting it tuned up, replacing some tubes more often, etc... now every time i take it in to my repair guy (who i don't know well) there is some new problem that costs me big time; i take GREAT care of my gear, so i just don't get it. i guess i just need some direction as to where to start learning about repairing my tube amp(s) myself. also, my current specific problem is completely random and continuous popping and crackling when my hotrod is up and running (tubes have little usage...maybe 15-20 max). i just don't want to take it to a guy that charges me $60/hour for labor when i can do it better myself!
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Old 18th October 2006, 01:33 AM   #2
PRNDL is offline PRNDL  United States
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Most likely it's in need of a "cap job", which is the replacement of the large capacitors in the power supply.

This isn't hard to do yourself, but it is quite dangerous because high voltages are stored in these caps (400-500 volts).

Fortunately, this is a very common repair and there's bound to be a lot of web pages describing what to do, and how to do it without something nasty happening.
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Old 18th October 2006, 01:44 AM   #3
anatech is offline anatech  Canada
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Hi juicy1484,
That is one young amp.

I look after a few vintage twins. They may need tubes and that's all. Your "service" guy may not know what he's doing, or is creating his own work for later.

A good service guy is your best friend. Your amp should not need any caps yet. It's easy to create all kinds of trouble, don't work on it yourself.

Now, your problem could be poor workmanship "down under", poor tube socket contacts or "not so good" tubes. For the old Twins, I use either 7581A's (beefed up 6L6GC) or 6L6EH from Electroharmonix. They stand up and sound great. If you have 5881's in there, put the proper tubes back in. (5881's only have a plate dissipation of 25W compared to a 6L6GC of 30W and 7581A/KT66 of 35W).

Given that your amplifier has been causing trouble for a while, find a known good technician, and use him.

One last comment. A good technician has a lot of training. He's actually worth more than $60 / hr, but normally doesn't get paid what he's worth. A bad tech gives everyone a bad name and isn't worth anything.

-Chris
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Old 18th October 2006, 02:10 AM   #4
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Hi juicy,

Repairing electronics is not something one can learn quickly in a few days or even months. However there are books that can help with the basics. I would suggest going to someplace like www.amazon.com and searching for "amp* repair". I just did and a lot of curious titles come up. Try eBay too as well as a general google search.

Also, even though your tubes are fairly new, they could still be the cause. I have little faith in some of the import tubes being sold today.

Victor
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Old 18th October 2006, 05:16 AM   #5
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I've run across the problem of seriously bad crackles and pops on a Fender Twin Reverb 100W job belonging to one of the engineers I work with. He gave it to me to fix coz he knew I was into tube stuff and he was sick of what passes for a professional service at the local guitar shop. In that case it turned out to be output tubes with partially melted screens. Fenders run very high voltages and the older onesused 470 Ohm 2 Watt CARBON resistors to each output tube screen. These resistors go very noisy and drift massively in value. Replace the 470 Ohm 2 Watt carbon resistors with 1K 5W wirewound resistors. This is one of those s"standard" mods that all amp techs "in the know" do routinely but your official Fender Serveman won't. If the screens have been overstressed badly then you may have to change output tubes again, even if there isn't many hours on them. Best option for 6L6 Fenders is Winged C Svetlana 6L6GC. Cheaper but almost as good is the JJ 6L6GC. If as your post suggests, the amp has had a new set of output tubes recently then they may be OK BUT check those screen resistors. They may well be your problem.

Cheers,
Ian

P.S. If you want to get some books to learn about tube amp service then do a search on "London Power". There you will find "The Ultimate Tone" TUT Volume 1 and Volume 2 by Kevin O'Connor. Those 2 books will teach you heaps about how tube amps work and servicing and modifying your own tube amps.
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Old 7th February 2007, 04:21 AM   #6
Nixie is offline Nixie  Canada
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gingertube, an acquaintance of mine has in his post-2000 made Fender DeVille also loud crackles and pops even when only the output stage is driven (plugging into the power amp input, which disconnects the input stages). I replaced all tubes, no change. Also since I'm bypassing the input stage that way, doesn't seem to be the problem of input connectors breaking their solder join with the PCB, which I've read about elsewhere for this model. Tilting the amp or moving it about tends to change the frequency of occurrence. I tried jiggling the tubes and tapping various parts, but didn't seem to be able to provoke the crackling this way (interestingly, connecting the probes of my multimeter to the B+ filter caps would create pretty much the same pop sound). I don't see how it could be the screen resistors since I put in brand new output tubes. No visible damage to any components. Any other suggestions?
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Old 7th February 2007, 05:49 AM   #7
Nixie is offline Nixie  Canada
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Schematic: http://www.fender.com/support/amp_sc..._Schematic.pdf
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Old 7th February 2007, 02:14 PM   #8
anatech is offline anatech  Canada
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Hi Nixie,
Resistors can often look just fine, but be bad. Don't trust your eyes! Measure the darn things. Also, they may be noisy without any outward signs. Tapping and a little freeze spray may allow you to find the defective part if you must. I will generally just change them if I suspect a problem. I always measure them and change them if they have drifted much.

-Chris
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Old 7th February 2007, 03:42 PM   #9
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I've repaired a number of Popping and Cracking Hot Rod Deville's Hot Rod Deluxes, Blues Deluxes etc...

Pretty much every instance the problem was the Plate resistors on the Phase inverter. I tend to rebuild the entire phase inverter with higher quality resistors and caps for assurance that that area is not going to be a problem...
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Old 7th February 2007, 04:57 PM   #10
Nixie is offline Nixie  Canada
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Interesting. OK, I'll check that. Thanks.
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