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FDP Forum / Amp Mods, Repairs, and Projects / Hot Rod Deville Loud Hiss/Crackling

Previous 20 Messages  
STR87

Panama

Nov 21st, 2017 10:22 PM   Edit   Profile   Print Topic   Search Topic

Thanks W,
I saw C60 a little chipped off, will change it. It's 220pf cap, any idea what is the voltage rating on that cap?
I'll be opening the amp guts on TG to do some checking. will post results on my finds!

willie
Contributing Member
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Too Near Atlanta GA

Amp Tech Emeritus
Nov 22nd, 2017 07:40 AM   Edit   Profile   Print Topic   Search Topic

I'm not seeing any reference to a C60 cap in the tech manual we have on file for the HR Deville.

w

STR87

Panama

Nov 22nd, 2017 09:36 AM   Edit   Profile   Print Topic   Search Topic

Yes that's weird. I started looking and it's on the new Hot Rod Deville III revB schem!

STR87

Panama

Nov 22nd, 2017 09:38 AM   Edit   Profile   Print Topic   Search Topic

Sorry it's C61

STR87

Panama

Nov 22nd, 2017 09:49 AM   Edit   Profile   Print Topic   Search Topic

SORRY AGAIN C60! what's the purpose of this cap, why it's added on the new boards? Could it be my problem?

STR87

Panama

Nov 22nd, 2017 12:29 PM   Edit   Profile   Print Topic   Search Topic

QUESTION:
Did some thinking and got to this conclusion.
If i still get the noise without V1 and i can dial out the noise with the eq ( treble, bass, mid) at the off position. Looking at the schematic, the problem then has to be between V1B plate exit and V2A input right? Or are there other possibilities?

willie
Contributing Member
********

Too Near Atlanta GA

Amp Tech Emeritus
Nov 22nd, 2017 03:12 PM   Edit   Profile   Print Topic   Search Topic

Yes, I found the more recent schematic...I was thinking your amp was more likely one of the newer issue ones. I have no time on this amp as it came out after I retired. I can see several of these 220pF caps added to the ground connections on some of the jacks. I don't know exactly what their function is but would guess that they are there to drain off static charge or some degree of hum that might have been an issue in earlier models. Regardless, I doubt they would be the cause of the symptoms you are experiencing.

You assumptions are likely correct but indeed there are other possibilities...such as the phase inverter plate loads.

w

STR87

Panama

Nov 22nd, 2017 03:34 PM   Edit   Profile   Print Topic   Search Topic

Thanks W,
I just could't resist and opened the amp up to check under the board, Joints seem fine except for the Master pot which is missing a little solder in one lug. The BASS pot is giving me a weird reading of 130k, so i'll be replacing it with a 250k, will change R12 also to 100K. Replacing C60 with a new 220pf 50v cap. Touch up on a couple of joints also, maybe i'll get lucky!


STR87

Panama

Nov 23rd, 2017 11:19 AM   Edit   Profile   Print Topic   Search Topic

UPDATE:
Did the changes above but no luck!
Waiting for the plate resistors to arrive and will give it a try.

willie
Contributing Member
********

Too Near Atlanta GA

Amp Tech Emeritus
Nov 23rd, 2017 12:56 PM   Edit   Profile   Print Topic   Search Topic

Let us know when you get those in and installed, although honesty compels me to say that knowing that your amp is the newer version, I doubt that the PI plate resistors would still be an issue. It was indeed a common fault in the early models.

That said it sure won't hurt to get those changed just to rule it out. Final fix is often something not quite as obvious or technically indicated.

I sure didn't mean to take over this thread...there are some fine members here that might have more recent knowledge of this particular model of amp, and for sure have already given some fine advice. Hopefully they will continue to follow this thread and contribute more as things progress.

willie

(This message was last edited by willie at 03:03 PM, Nov 23rd, 2017)

Peegoo
Contributing Member
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Roisin, I wanna

fight your father
Nov 23rd, 2017 02:01 PM   Edit   Profile   Print Topic   Search Topic

Process of elimination!

Please keep us posted.



STR87

Panama

Nov 29th, 2017 03:07 PM   Edit   Profile   Print Topic   Search Topic

UPDATE:
Did some checking around the tone stack and found that:
All eq's at 0 i get 0vdc on R8 (grid resistor of V2A) but when i move the dial of any eq up i'm getting up to +3vdc on R8.
Is it ok?



pdf64

UK

Dec 1st, 2017 02:28 AM   Edit   Profile   Print Topic   Search Topic

Most likely a tone stack cap leaking dc, C5,6 or 7 of linked schematic.

HR Deville - correct version?

STR87

Panama

Dec 1st, 2017 07:00 AM   Edit   Profile   Print Topic   Search Topic

The schematic is correct.
I did change the treble and bass cap a while ago C7 to a 250pf Silver mica and C5 to .1 Orange drop cap.
I suspect the SM cap being faulty, will change it over the weekend.


pdf64

UK

Dec 1st, 2017 12:24 PM   Edit   Profile   Print Topic   Search Topic

I've seen reports that modern silver mica caps may be prone to heat damage during soldering.
Mitigation is to use a heat sink (eg a croc clip) on the leg between the joint and body, and to be quick!

STR87

Panama

Dec 3rd, 2017 09:16 PM   Edit   Profile   Print Topic   Search Topic

GOT IT!!!
It was the treble cap all along bleeding some DC volts. Thanks everyone for your help.
I also did some mods which are sounding very good, cut off r105, changed C6 to 0.047uf orange drop and changed C1 to 25uf sprague cap.
It cleaned the amp and made it more responsive, it has overall less bass and low mids.


pdf64

UK

Dec 5th, 2017 04:54 AM   Edit   Profile   Print Topic   Search Topic

Yey, well done!
Doesn't cutting out R105 mess up the channel/boost switching?
To get more control over bass, another mod is to link out the wiper and hot / CW terminal of the mid pot.

STR87

Panama

Dec 6th, 2017 12:26 PM   Edit   Profile   Print Topic   Search Topic

Everything is working normally. Forgot to mention that i changed the Mid pot to 10KA and jumpered the two terminals. I also have a switch which disconnects the negative feedback, i use it when i want and earlier breakup and more high frequencies through.
I got to try it at a gig yesterday, first impressions:
* Later breakup, cut down on the overwhelming bass and low mids.
* better reverb
* Dirty channel is more trebly (really don't mind since i don't use it).

I need the amp to cut more through the mix, have to get rid of those low mid freq. Any ideas? (looking forward on keeping blackface specs)

pdf64

UK

Dec 7th, 2017 04:07 AM   Edit   Profile   Print Topic   Search Topic

R12 is still 130k?
A regular BF would have C24 (V3 LTP input coupling cap) as 1nF (rather than 22nF); that would help to cut a bit of low end 'woofiness'.

(This message was last edited by pdf64 at 06:08 AM, Dec 7th, 2017)

STR87

Panama

Dec 13th, 2017 08:04 AM   Edit   Profile   Print Topic   Search Topic

R12 is 100k.
I might try lowering the bass cap first from .1uf to .022uf. I'm trying the amp a couple of days now in a band situation and i've noticed i lost a lot of mids.


Previous 20 Messages  

FDP Forum / Amp Mods, Repairs, and Projects / Hot Rod Deville Loud Hiss/Crackling




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