Peavey Classic 30 Issues

nick · 2010-03-16T19:28:59+00:00

I took my amp to Graemestock where it got a bit of a workout by Cannons band and whoever else jammed. Then took it to the Farm Blues jam, brought it home and dumped it in the room. Set it up and turned it on and when I do the speaker emits loud cracking noise and the wall behind the amp was lit up with blue and orange lights. Switch it off, swing the amp around and turn it on again and one of the valves is going ballistic, bright yellow and blue lights coming out of it, the rest not even lighting up. not my amp but looks exactly the same, its the valve on the far left, one of the 4 large EL84s (Sovtek) Any ideas? ☹

nick

F2 is the heater fuse so must be a bad set of power valves (I hope). New fuse, new valves and try again ☹

TomCat

nick wrote

Amp runs fine for a while, switch it off leave it to cool down. Come back about an hour later turn it on and it starts humming and then two valves glow twice as bright as the others..

Looks to me like the biasing on one side is up the spout, possibly a biasing resistor that has gone US or a bad solder joint seeing that it happened after the amp was transported.

Time for a tech to look at it and find out what is wrong there.

nick

TomCat wrote
nick wrote

Amp runs fine for a while, switch it off leave it to cool down. Come back about an hour later turn it on and it starts humming and then two valves glow twice as bright as the others..

Looks to me like the biasing on one side is up the spout, possibly a biasing resistor that has gone US or a bad solder joint seeing that it happened after the amp was transported.

Time for a tech to look at it and find out what is wrong there.

After this picture I switched the valves around and then only a single valve was glowing bright and it was then second from the left.. Then the tube started going nuts and the fuse blew

Karel-Mars

Where is Matt and Karel? Probably rolling some tubes and smoking some amps in the workshop 8)

That blue glow does look unsettling. Note: the fuses used in tube amps are special. SLOWBLOW fuses are what you need. Get them from electronic shops. They cost a bit more than the fast blow types which are more common. Like someone said; get ten.

Tubes are not necessarily your problem though. The vibrations/heat in combos causes cracks to appear in the solder joints that are on the pcb. A good tech should be able to scan the pcb and resolder the bad joints.

Tubes are vulnarable to damage when some of their connecting points are not connected, especially the input grid (through which the fixed bias voltage appears). Rather switch off till you get it fixed ?

nick

Karel Mars wrote Where is Matt and Karel? Probably rolling some tubes and smoking some amps in the workshop 8)

That blue glow does look unsettling. Note: the fuses used in tube amps are special. SLOWBLOW fuses are what you need. Get them from electronic shops. They cost a bit more than the fast blow types which are more common. Like someone said; get ten.

Tubes are not necessarily your problem though. The vibrations/heat in combos causes cracks to appear in the solder joints that are on the pcb. A good tech should be able to scan the pcb and resolder the bad joints.

Tubes are vulnarable to damage when some of their connecting points are not connected, especially the input grid (through which the fixed bias voltage appears). Rather switch off till you get it fixed ?

I bought 5 250v 1a slowblow fuses from Mantech during lunch, a whole R4. Im going to put in a new fuse and try out the 2 new tubes I have and if I cant find a combination or it pops the fuse again can you have a look? ☹

nick

New fuse in, pre-amp valves in, power valves in, one arc's hectically inside the tube, swop that one out with the spare other 3 and its always that tube. Need a single EL84 thats working to confirm this, still dont see how 3 tubes could randomly die without something upstream causing it ☹

FenderBender

+1 Karel

3 tubes behaving the same way is indicative of something else being wrong, more than likely bad joints, as you mentioned.
I had a Peavey in a little while back with loads of dry joints and a few hairline cracks between the tracks and the solder pads due to hot and heavy components shaking loose during transport.

[deleted]

In other words, the blues jam killed your amp, Nick. Which is...more fodder for the next blues jam!

FenderBender

I took a look at the schematic for the classic 30 and F2 (1A) is actually on the HT supply for the tubes, so we're onto something.

nick

Graeme Parfett wrote I took a look at the schematic for the classic 30 and F2 (1A) is actually on the HT supply for the tubes, so we're onto something.

Cool, shout when I can drop it off, live really close to you ?

FenderBender

Check your pm ?

singemonkey

Stratisfear wrote In other words, the blues jam killed your amp, Nick. Which is...more fodder for the next blues jam!

My ol' tweedie, she used to sing like a tweedie bird
Yeah my ol' tweedie, used to sing like a tweedie bird
But her bottles got hot, I never thought, but now my tweedie bird's unheard. [miserable turnaround]

FenderBender

And ol' Tweedie sings again ?

After removing the valves, stripping the amp down, removing the 3 part PCB and examining, I noticed several dry joints and slight traces of an acidic residue on the board. After a passive test (with the old Fluke multimeter) of the entire HT power supply, tube output section, output transformer, speaker and phase inverter components to ensure they all still measured within limits, I carefully inspected the electrolytic caps to ensure that none had leaked. Testing involves desoldering and removing one lead of some of the components (so as to obtain accurate readings) and then resoldering those components into the PCB.

I decided to turn the board over and resolder all the remaining dry joints. During manufacture, the single PCB with breakable tabs is soldered before being broken into 3 boards and there are several wire links connecting them together along two 90 degree bends. Most of these solder joints, as well as others on the PCB, were badly pitted. The acidic residue was concentrated at larger solder areas on the PCB. I concluded that this was flux probably due to a fault in the solder process in the factory or their choice of solder. The amp also runs hotter than most, which probably has a bit to do with it. I ended up resoldering 75% of the PCB and then decided to perform a live voltage test on all the power supplies and all tested good.

Then I inspected the valves that were in the amp. Two looked ok, but the shiny barium flash on the inside of the other two had turned a matt grey colour when viewing it while looking inside the valve from the pin side. There were also slight burns on the inside of the glass adjacent to the rectangular windows in the plates. This meant that serious electrons had been gushing through the plate and struck the glass envelope. I checked the spares. One looked spanking new and the other showed slight greying of the internal layer of the barium flash, but no burns on the plate. I popped in the original preamp valves and an old trusty quad of rattly and slightly microphonic EL84s that I are in my workshop and fired her up. I'm still a bit deaf, but damn it was fun! I found it to be an extremely versatile amp with good cleans and some ass kicking overdrive to boot! I played her for a good 4 hours in total, switching off every 30 minutes and on again after a cooldown period of 30 minutes.

So Nick, I'd say it's time for a new quad of JJs and I suggest replacing the 12AX7s in the preamp as they are getting a little noisy. JJ's ECC83s sounded great in Manny's Delta Blues. Adjusting the bias on the power tubes is not essential as your amp has a fixed cathode bias, but can be done with a small trimpot mod if you really want it.

aja

It is a shame that these amps have been so poorly manufactured. I have heard from different amp techs the same story about the quality control.

They really do sound fantastic though!

AlanRatcliffe

It's strange, but the Classic 30 seems to go through phases - different batches with varying reliability. The original tweedies seemed pretty bomb proof and reliable (I used one for quite a while), then they were redesigned and "improved" (when they started coming out with tolex or Tweed covering) and every second one was breaking down. Then they seemed to get a handle on that for a while. But recently I'm hearing of more problematic ones again. Pity... they are great amps - packing a lot of punch for the size and weight.

FenderBender

I had similar issues with a 5150 and will be sorting another Classic 30 with similar issues this week. So yes, it seems Peavey has a few issues with QC.

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