JCM800 problem any ideas?

[Georgiatec]

Just had my JCM800 4211 combo serviced and completely re-valved with a full set of JJ's apart from a Tung Sol in pos. 5 in the preamp. Problem is the boost channel is now so much quieter than the normal. Is this right?. The tone of the amp is fine but it just doesn't produce the volume a 100 watter should do, without going into feedback with my LP. I'm struggling to cut it with the rhythm guitarists valvestate 100 combo. Any and All ideas/solutions welcome.

settings I'm using are;

Normal.......Vol...3.5, Treb....full, Bass....5

Boost......Gain.....7.5, Vol......7.5, Treb....9, Mid.....4, Bass... 5

Master......Vol.....4, Pres...5.

Cheers guys.

 

[Frankie]

Well if it was loud before the tubes, and now with the new tubes it's not loud, I think you have a pretty good starting point to test. Put the old tubes back in and see if it wakes up. Are you sure your tech didn't accidentally install a lower gain tube in one of the preamp sockets? I used to have a 4211 and with the gain channel on 7.5/7.5 you should be stone cold deaf. That amp was fucking LOUD!

 

[Jethro Rocker]

Yep, switch back especially V2, V3 I think, and see. The "without going into feedback" makes me wonder if one tube is microphonic - way more feedback at lower volumes is one symptom.

 

[Frankie]

Is the normal channel still the same volume that it used to be and just the boost channel is quiet?

 

[Sir Crunch A Lot]

Take one of your older tubes and replace each position with it to see if you have a bum tube. I hate jj's for there reliability.

 

[Georgiatec]

The Normal channel seems the same, if not a little louder. Picture of the 5 valves that came out...trouble is I don't know what position each one was in apart from the Marshall branded valve was in pos.5.

There are 3 TAD valves one unbranded and one Marshall branded

 

[Sir Crunch A Lot]

Position of the Preamp tubes does not matter. You can mix and match the order and brand.

 

[Jethro Rocker]

Yep, I agree, start by replacing V1 Tube closest to input, furthest from power tubes) with one of your old tubes (any one) it's likely OK since your clean channel is fine. Then go to V2 etc and you should be able to find which of your new tubes is shot...

 

[Georgiatec]

Thanks guys...I'll post if it sorts it out or not.

 

[Georgiatec]

Ok working all week so not had time to try it. I noticed a background fizzing sound after playing certain notes (D seemed the worst) as well as the lack of volume. Decided to do the pencil test on the tubes V3 pre amp tube makes a nasty popping sound when tapped. I've tried 5 different tubes in this position all pop to some extent...does this mean the tube socket is buggered?. I've managed to stop the fizzle sound when playing by bending the pins of the tube inwards slightly so it fits more tightly....but am I just putting off the inevitable spend on new sockets and am I better off changing all 5 while I'm at it? I think mu local amp tech. my be taking the piss as I'm already into him for 100 pounds (160 bux) and he hasn't spotted this problem. I'm sure any tech reading this would have found this issue if they were giving an amp a service and re-valve.

Again any help/advice you can offer would be appreciated.

 

[Georgiatec]

Anyone?...Just been to rehearsal today and had to stop using the amp. After playing for 5 mins the amp made a loud buzzing noise. If a belted the top of the amp the noise stopped then soon came back as the vibration made the tube connection fail. I ran the amp breifly without the V3 tube in and no buzzing so problem is obviously tube socket No.3
So am I better off replacing all 5 pre amp sockets or just the faulty one?...or can this be cured without replacing the socket?.

 

[JayCM800]

Did you try spraying some cleaner? Without getting shocked and all that...

 

[Georgiatec]

Thanks Jay...I sprayed some on the pins of a valve and then worked that in and out of the socket....would you recommend taking the amp out of the cab and spraying more thoroughly then allowing to dry?.

 

[JayCM800]

Thanks Jay...I sprayed some on the pins of a valve and then worked that in and out of the socket....would you recommend taking the amp out of the cab and spraying more thoroughly then allowing to dry?.

Since i am not a tech, the sensible approach would be to spray the pins on a tube and seat it and unseat it from the socket a couple of times...If that doesn't work take it to someone who knows what he's doing! But i'd hate to pay "bench rate" for an amp tech to do this same stuff!

 

[Georgiatec]

Sorted it...it was definitely the socket on v3. I removed the amp from the cab and gave v3 socket a good blast with IPA....working it into the pin sockets with a very small pipe cleaner. Left it to dry for an hour, valves back in, fired her up and she's as quiet as an angels fart....sounds sweeter too. V3 is the main gain valve on the boost channel so I must have been loosing tone as well as power before. On close inspection the valve sockets seemed to have spread a little and the valve was a sloppy fit. I've put a very slight kink in the pins of the valve and they seat nice and tight now.

Happy days!!

 

[surface54]

i thought it would been the Tung Sol in v5..glad you got it sorted

 

[ironlung40]

it's amazing what a little contact cleaner will do isn't it?? Wow!

 

[Georgiatec]

i thought it would been the Tung Sol in v5..glad you got it sorted

The Tung Sol was a little dicky...so I changed that for a TAD. I was recommended to put the TS in v5 to smooth the tone out but putting the TAD in there seems to make the decay even smoother so a result all round. I now have JJ's in v1 - v4 and the TAD in v5. I just hope when I next play at volume it doesn't all go pear shaped again.

 

[Georgiatec]

Although the pre amp tube problems are sorted I still seem to have the same volume problem on the boost channel. I played a gig last weekend and had the master dimed with the normal channel at 3.5.....I ran the boost channel with the gain at 9 and the volume at 8...I know this cannot be right. There are no problems with tone though...she sound great.