NO SOUND!!! HELP (VH4)

[Ventura]

Hello Diezel Comrades... Any idea as to WTF just happened? Playing on my VH4 about 2 hours ago - mellow, low volume, lovin' it (as I have every night since getting it). After dinner, turned it back on, lights powered up, waited a minute, plugged in, and flicked off the Standby - no sound. Cables are good - checked. Swapped out the cab - no dice (however cab works with my Soldano head), no fuse lights indicated on the back, all tubes warm and glowing. If I turn the master up, I can here a slight hiss through the cabinet - just as it were if it were being played, but it seems NO signal is getting to the amp from any of my guitars.

History. Had this amp for 10 days. Bought used in excellent condition. Swapped out all tubes 2 days ago (stuck with a matched quad of Winged C SED EL34s and replaced all preamp with high quality Tung Sol 12AX7s) and it has played like buttah since. All lights operating as to be expected, channels change, volumes are set at audible levels, no juice...

ANY ASSISTANCE WOULD BE REALLY GOOD RIGHT NOW!!!!!!!! Thanks...grrrrrrrrrrrrrrrrrrrrrrrrr...

V.

 

[Ailean]

If you are getting hiss at volume then it sounds like the power stage is working. I'd try replacing the preamp tubes one at a time, just because they glow doesn't mean they work.

I'd also try swapping out the power tubes in pairs, just in case.

 

[steve_k]

All power tubes lit up? If so, you've got no preamp. Check V1. Pull the tube and put an old one in. If you just changed them, you may have gotten a dud. Also, in the VH4, there is another fuse. Got to pull the chassis out. If the preamp tubes are glowing though, this fuse would be OK. Its sittin up there by the midi board.

Steve

 

[eh-D]

If you plug your guitar directly into the serial effects return do you get anything?

 

[Ventura]

Morning...

Thanks for the input here. So I was kinda freaking last night, and to get things "figured out", I ended up pulling the new EL34's out and replacing them with the old ones I just yanked a couple days ago. The sound was back. Played for a bit - no problemo. Then let it cool, put the new EL34's back in and same thing - no sound. So then put the old ones back, and after powering off and on a couple times, it came back to life. So - I've currently (no pun intended - heh heh) got the old EL34's in there working as they did before (Winged C SED). My new Winged C EL34 are back in their respective boxes awaiting either a technician or some profound news from this forum.

The preamps were indeed ALL replaced with new Tung Sol 12AX7's. If they were the culprits to this crapping out, would it not be strange that my sound came back with screwing around with the power tubes?

Secondly, as this amp will probably be going IN to a tech, what's the recommended plate current for Winged C SED EL34's?? I've read somewhere around 35mA to 40mA - this correct??

I'm frazzled.... And YES to one of the questions out there - they're ALL lighting up just perfectly. In fact, when the new EL34's go from standby to "run", the usual blue arc occurs inside them and they seem ready to roll!! Secondly, re: having tried the serial effects loop...not yet.

I'm a little concerned here. THANKS FOR ALL YOUR INFO!!!!!!!

V.

 

[Ventura]

AND!!!! Last but not least...

Can any of this tube nonsense actually hurt my Diezel or does this sort of crap tend to take it out on the tubes and the tubes alone?

Miffed. Worried. Wanting to play. Freaking out like a concerned father... I do love my VH4.

Namaste,
V.

 

[SpicedMuffin]

if you have the external bias points on your vh4 the bias should be
60-70Ma because you are bias both tubes in the pair

 

[Ventura]

Right. However, no external bias points. So this is a "pull the chassis" situation and the bias ought to be as you say, around 70mA to 80mA (thereby creating 35mA to 40mA per tube) IF my readings and so forth are correct.

I'll be mucking around with this again later this afternoon - right now it's too hot and sunny out to screw with it

ANY further assistance to this dilemma will be accepted with open arms. Any tech worthy of working on this is a day's trip for me to the city and back. Not cool. I am going to look into this "Tech Corner" to observe how to bias the amp myself. I've had extensive electronics training and practice in my time (16 year computer tech turned realtor). I've just never messed with actual amplifiers before, but if logic, a deft hand, and attention to detail are key, I can do this. I'm just nervous and NOT wanting my amp to sustain any long term damage because of what's happening.

V.

 

[Ventura]

PS...

Checked Tech Corner and am going to give this biasing gig a try sooner than later.

Judging from your replies - seems as though the preamp section is what caused the problem, but in my experiment to isolate the problem, it was swapping the power tubes that made the difference. SO - that's still a bit odd.

AVAGOODONE!!!!
V.

 

[steve_k]

PS...

Checked Tech Corner and am going to give this biasing gig a try sooner than later.

Judging from your replies - seems as though the preamp section is what caused the problem, but in my experiment to isolate the problem, it was swapping the power tubes that made the difference. SO - that's still a bit odd.

AVAGOODONE!!!!
V.

Email Peter Diezel. He wouldn't stand for this .

Steve

 

[Ailean]

PS...
Judging from your replies - seems as though the preamp section is what caused the problem, but in my experiment to isolate the problem, it was swapping the power tubes that made the difference. SO - that's still a bit odd.

Normally the power tubes work in pairs, so even if one pair goes down the other will carry on working and give you sound, so it's not a bad assumption to suspect the preamp stage if you lose all sound. It's just wrong in this case

 

[Ventura]

Posted this under another thread title... I installed the new ones, re-biased, and the obvious problem was that the 6L6 switch was engaged - NOT the EL34 switch. Apparently the old tubes worked due to their sensitivity but the new ones were too highly rated, so nada...ice cold...no juice.

AMPED!!!!!!

And again, thanks for all the assistance.

V.