Traynor amp blowin fuses

[W DeMarco]

hI fOLKS

Yesterday I changed the tubes in our yba 3 traynor bass head. Swapped EL34's for EL34's and ax7s for ax7s. Today its blowing fuses. 250 Volt 5 amp fuses. I dont get it? Any thoughts?

Will

 

[SSLtech]

Try the lab... May get better luck than the brewery.

 

[solder_city]

any thoughts? cause and effect, dude.

you put new tubes in, it starts blowing fuses.

ergo, the new tubes might have something to do with it.

if you put the old tubes back in, does it still blow fuses?

 

[W DeMarco]

I figured it might be the new tubes! Wondering if anyone had experienced this as well! SSL, I am still waiting to wire up my Dolby rack. When I get to it are you still interested in swaping a couple of mods for some help with the wiring?

 

[SSLtech]

Mods? :?:

Lemme know when you have a question or two...

Keith

 

[W DeMarco]

Mods = modules. Bad choice, no I am not planning on moding it! I want to wire it today but I have way to many projects on my desk to deal with it. The in outs seem easy enough I think I am more worried about the record logic. My deck is a MX80 Otari, Im wondering what kind of multi pin connector the logic connections terminate to at the deck.

 

[amorris]

Old tubes???? put em back in?????

 

[W DeMarco]

Traynors at the studio, Im at home. I guess I can put the old ones back in but it sounded so nice. Plus with the tube change it got much louder. Used to crank it to about 5, new tubes have it just as loud at 2.

 

[amorris]

so it doesnt blow immediately?

put all old tubes in. replace 1 at a time till it blows.

 

[W DeMarco]

Yeah its strange. When I first fired it up it was amazing. I let them burn for quite a while. Maybe 5 hours. Then out of the blue it started poppin fuses. Replace and play for a while then bam, again it blows. I'll try the replace one at a time and report back.

Thanks!

 

[Mbira]

Did you switch the impedance switch on the back of the amp (if there is one)? Being just as loud at 2 as it was at 5 is not really a good sign to me. You are drawing too much current (obviously). Check that impedance thing. Did you bias after switching tubes?

 

[solder_city]

first put ALL the old output tubes (EL34) back in, and see if it still blows fuses.

if it is a tube problem its gonna be one of the power tubes. i have never seen a preamp tube (even a total failure) pull enough current to blow a fuse. its not even possible in most circuits unless youre talking about a heater short, which i have not seen.

 

[Gus]

As others posted I would check/change the output tubes.

What brands before and after?

Output tubes idle current with old tubes and output tubes idle current with new tubes would be helpful.

Do the plates glow red with the new tube el34s?

Do you know how to bias a tube guitar amp output stage?

 

[abby normal]

Most likely an output tube.

 

[W DeMarco]

[quote author="Gus"]As others posted I would check/change the output tubes.

What brands before and after?

Before mix and matched oldies GE, Zenith...

Output tubes idle current with old tubes and output tubes idle current with new tubes would be helpful.

Do the plates glow red with the new tube el34s?

plates seemed alright

Do you know how to bias a tube guitar amp output stage?

Ive biased my super reverb before

[/quote]

Thanks Gus

 

[W DeMarco]

[quote author="Mbira"]Did you switch the impedance switch on the back of the amp (if there is one)? Being just as loud at 2 as it was at 5 is not really a good sign to me. You are drawing too much current (obviously). Check that impedance thing. Did you bias after switching tubes?[/quote]

No switch,

Thanks Bud!

 

[walter]

It may be a bias issue. Check the bias and adjust it as needed. Also check the screen resistors. You can also check the resistance of the output transformer primaries, if both sides are more than a few ohms different, there could be a shorted winding. After installing new tubes, I like to crank the amp and run signal through for awhile to see if a tube will redplate.

 

[CJ]

rock star approack, crow bar the fuse, watch very carefully, listen and smell as fast as a 3 second duty cycle ill allow, or suffer the brewerry for anothert three weeks.

 

[ProfPep]

Look at the output valves. Any red patches on the anodes? If so it's likely a screen feed resistor, going high or open circuit. An old valve socket can have a tag snap off when you change a valve. I don't know the Traynor insides, but if the screen feed resistors are directly wired to the valve socket, this is a possible scenario. A dirty/bad pin socket is another possibility.

Screen is Pin 4

If you have had previous damage, there can sometimes be flashover, (with Bakelite sockets), burning the plastic between pin 3 (Anode) and screen, (pin 4). You can do a temp repair by removing the carbonised bakelite with a fine point tool, but the long term solution is a new valve base, (preferably a ceramic one!) You often got this one from guitarists balancing a drink on top of the amp and splashing beer into the inside. sometimes they shattered the valves, sometimes they got it around the sockets, then the amp went bad a night or so later

Another symptom is a blue glow (UV) on power.

I've had new (cheapo) EL34's which were gassy enough to cause problems like this after a short while, I think you get accelerated internal leakage.

Lie the guys say, start by putting the old output bottles back in, and substitute from there.

HTH

Mike

 

[W DeMarco]

Much appreciated fellas. Ive begun the debugging. I quess I should bring the beast home to make it less painful.

Thanks again for the input guys!

Will