Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Colas LeGrippa on January 30, 2013, 11:28:08 am

Title: Fender HOT ROD De Ville
Post by: Colas LeGrippa on January 30, 2013, 11:28:08 am: Hi,

this amp just came in for repair. The problem is a permanent light squeal on the ''more drive'' channel. I've checked the bias, replaced the 12ax7's, chopsticked and did all what I was trained to with no results. Any idea ?

Thanx

Colas
Title: Re: Fender HOT ROD De Ville
Post by: sluckey on January 30, 2013, 11:47:52 am: Colas, you are seeing a lot of amps lately. Have you started a repair business?
Title: Re: Fender HOT ROD De Ville
Post by: Colas LeGrippa on January 30, 2013, 01:43:49 pm: Quote
Colas, you are seeing a lot of amps lately. Have you started a repair business?

Yeah, well for the moment I stay home so all I have to do is play my guitar and fix amps. ( yes my darling and do the dishes :icon_biggrin: ). I realize that fixing amps especially the PC boards ones is not easy with only a Multi meter and my ears. If I don't go on tour within the next few months, I will try buying a scope. It will keep me busy for a couple of months more, just trying to figure out how it works !

Colas
Title: Re: Fender HOT ROD De Ville
Post by: plexi50 on January 30, 2013, 07:43:24 pm: Do you have or have you built Dougs listening device? I dont know how i did without it all of my previous years. Dont need to use it a lot but when you get a squeal or crackling going the listening device is the Doctor. No Co Pays either
Title: Re: Fender HOT ROD De Ville
Post by: Colas LeGrippa on January 30, 2013, 09:06:57 pm: Quote
Do you have or have you built Dougs listening device?

is it a probe with a 600V cap , the other end being amplified by a small amp ?
Title: Re: Fender HOT ROD De Ville
Post by: stratele52 on January 31, 2013, 03:46:39 am: Hi Colas ,

If these amp use ribbon cables , these cables must be at the "right " place . Moving them could brig you some noise and probably squeal (?)

Try to push or pull them with power ON and heard ....

Good luck
Title: Re: Fender HOT ROD De Ville
Post by: mageerc on January 31, 2013, 06:58:10 am: Usually that squeal has something to do with those 470 ohm 5 watt power resistors having a cold solder joint... here's a good link:

http://www.justinholton.com/hotrod/ (http://www.justinholton.com/hotrod/)

I realize the text is referring to a Hot Rod Deluxe, but these amps share pretty much the same board...
Title: Re: Fender HOT ROD De Ville
Post by: Danskman on January 31, 2013, 09:02:31 am: I fixed a bunch of HRD and Blues DV or DL. Most of their problems are due to bad solders (a lot!), bad tube sockets, bad input jacks (a lot!!).
To gain access to the copper side of the circuit, you have to:
- pull the amp off the cab
- dismount the knobs
- dismount the pots and jacks nuts
- write down the wires connections (CPxx - wire color) on left side of the PCB
- disconnect these wires
- unscrew the PCB
- gently pull the main PCB back
let's go for the debug...
HTH,
Danskman
Title: Re: Fender HOT ROD De Ville
Post by: Colas LeGrippa on January 31, 2013, 12:08:15 pm: yeah I know I have redone part of the toasted circuit on a blues deluxe. it takes 45 min to access the pcb board solder side......compare to 5 min on a point to point !

Colas
Title: Re: Fender HOT ROD De Ville
Post by: plexi50 on February 01, 2013, 10:18:50 am: Quote from: Colas LeGrippa on January 30, 2013, 09:06:57 pm
Quote
Do you have or have you built Dougs listening device?

is it a probe with a 600V cap , the other end being amplified by a small amp ?

Yes* It makes the difficult to locate noise problems easy to find.
Title: Re: Fender HOT ROD De Ville
Post by: Colas LeGrippa on February 01, 2013, 04:51:27 pm: sure, where woudl I be without it ?

( doin' the dishes in a Mc D ???? )