No amp tech within 6 hours, I need some help please!!

daveanto21

Gold Supporting Member
Messages
1,141
Hey guys,
I got a bluetron blueverb delivered today and am having some issues. I am hoping you guys that are far more educated than me can help point me in the direction of the issue. Here is the skinny:

It was delivered without tubes installed but they were all clearly marked.

I put the tubes into their respective slot.

The power tubes are kt77 gold lions and is what the amp came stock with.

When I put the amp into standby the kt77 closest to the rectifier tube wasn't glowing very bright, or possibly at all. I remember reading that some tubes may glow less bright due to heater differences so I thought it would just sound like crap if it had a tube that was going out.

Either way, when I went to turn the amp on it just made a loud pop, similar to when my fender 68 custom deluxe is being turned off.

The amp lost power so I checked the fuse which was blown.

I checked pins 2 and 7 (heater pins) on the kt77 and it does have continuity.

What should I check next?
 

Jeff Gehring

Gold Supporting Member
Messages
6,177
Are you CERTAIN you loaded the tubes in the sockets correctly? As in, yes, I directly observed the socket and aligned the pins correctly before insertion?

With certain octal sockets, it is really pretty easy to insert the power tube incorrectly, so the keyway is not aligned with the slot for it in the socket. This could account for your blowing a fuse if you got 'lucky' with your misalignment.
 

daveanto21

Gold Supporting Member
Messages
1,141
Are you CERTAIN you loaded the tubes in the sockets correctly? As in, yes, I directly observed the socket and aligned the pins correctly before insertion?

With certain octal sockets, it is really pretty easy to insert the power tube incorrectly, so the keyway is not aligned with the slot for it in the socket. This could account for your blowing a fuse if you got 'lucky' with your misalignment.

It was definitely pushed all the way in and flush. I am pretty positive that I did, otherwise it would not have went in all the way in... right?
Thanks for answering Jeff!
Dave
 

rh

Robo Sapien NoiseMaker
Platinum Supporting Member
Messages
6,913
It was definitely pushed all the way in and flush. I am pretty positive that I did, otherwise it would not have went in all the way in... right?
Thanks for answering Jeff!
Dave
It's possible for it to go all the way in and flush because the keyway wasn't aligned and it broke off as you inserted the tube.
 

daveanto21

Gold Supporting Member
Messages
1,141
You guys nailed it. The keyway tab was broken off. I was aligned 1 or 2 pins off. The tab didn't break from me, possibly in shipping, possibly it was already like that. I just looked at the other power tube that is not broken and saw where the pilot tab was. The amp is warming up now! All tubes are glowing.....and I plugged the speaker cab up! Thanks Jeff and rh. Thank you for taking the time. Now I am keeping my fingers crossed it didn't hurt anything other than the fuse!
 

Motterpaul

Tone is in the Ears
Messages
12,936
Glad to hear you did not blow up the tube or anything in the amp. Yes, it is a little too easy to insert an octal tube incorrectly.
 

daveanto21

Gold Supporting Member
Messages
1,141
Well crap guys, maybe I wasn't so lucky...... after getting about 1 hour of playtime on it the fuse blew. It didn't make any noise or do anything spectacular. Just lost power.

The fuse was blown when I pulled it. I figured maybe the fuse was weak, after all, it was laying in the local music store owners tool box forever.

I bought new 2.5 amp slow blows and put one in. This time I only got 10 minutes or so before the fuse blew and I lost power.

At this point something is up. It definitely feels like it is heat related. After it blew I quickly smelt and looked behind the amp. The heat seemed possibly high for the 10 minutes of play time and the smell seemed "hot" and had a slight odor. No smoke or anything like that.

Should I get a new set of Power tubes knowing that one was damaged in shipping and or may have been damaged when I put it in a pin over?

Thanks for all the help guys!
Dave
 

79Stone1

Member
Messages
245
I've done the exact same thing and if the power tubes worked at all afterward they never lasted very long. If you're comfortable measuring voltage inside a live amp, you could remove the power tubes, install a fuse and measure all the voltages. They should all be higher than normal under when no power tubes are present. If they come out low or if the fuse blows under this condition, you gotta stop and have it looked at by a tech because the circuitry inside the chassis has been damaged. I think it's fairly likely though that you have a power tube that cooked itself and started drawing too much current and eventually blew the fuse. Plan to replace the power tubes for sure, and I'd want an extra rectifier tube on hand too.
 

J M Fahey

Member
Messages
2,370
^^^^^^^ that.
Given your 6 hour driving distance, try fitting new tubes first.
I would turn amp on *outside* of the cabinet, on a teble over some books or wood blocks so you see the guts, turn it on and watch it carefully for 10 or 20 minutes so as to catch any smoking, toasting, sparking, whatever.

If anything like that, I´d pack the amp and send it to a Tech.

*Literally* 6 hours away from nearest one?
No closer related techs, say HiFi/TV/DVD/Home Theater guys around?
Not their specialty but if they can repair regular stuff, have test instruments and tools, etc., maybe one can be guided to repair an unfamiliar (to him) Guitar amp.

Tube amps are relatively "easy": circuits are classic, "everything is visible", they are relatively robust, meaning a tube can stand a short or lack of bias (for a few seconds enough to notice) while SS amps can die in milliseconds and damage a lot of direct coupled parts.
Just a suggestion.
 

gldtp99

Member
Messages
3,828
Yes, I'd put my money on the problem being the one output tube that was installed improperly dying

Maybe a fresh set of output tubes is all that's needed to put the amp back in operation

Maybe there's nothing else wrong with the amp

And maybe there are more problems

But first try a new set of output tubes and see if that fixes it
 

daveanto21

Gold Supporting Member
Messages
1,141
If I get a new matched set of gold lion kt77's (current tubes) will I need to bias the amp? Or can I just put them in and go? It is like a super reverb / Dumble style build.
 

79Stone1

Member
Messages
245
If I get a new matched set of gold lion kt77's (current tubes) will I need to bias the amp? Or can I just put them in and go? It is like a super reverb / Dumble style build.
Yes. The bias conditions should be checked. As a part of the procedure I described earlier, measuring the voltage at each power tube pin with no tubes installed would provide a lot of cursory information like whether the bias circuit is functioning, among other useful information.
 

daveanto21

Gold Supporting Member
Messages
1,141
Yes. The bias conditions should be checked. As a part of the procedure I described earlier, measuring the voltage at each power tube pin with no tubes installed would provide a lot of cursory information like whether the bias circuit is functioning, among other useful information.
I can absolutely do that. I am fairly competent with a multimeter and basic electric systems.
 

daveanto21

Gold Supporting Member
Messages
1,141
^^^^^^^ that.
Given your 6 hour driving distance, try fitting new tubes first.
I would turn amp on *outside* of the cabinet, on a teble over some books or wood blocks so you see the guts, turn it on and watch it carefully for 10 or 20 minutes so as to catch any smoking, toasting, sparking, whatever.

If anything like that, I´d pack the amp and send it to a Tech.

*Literally* 6 hours away from nearest one?
No closer related techs, say HiFi/TV/DVD/Home Theater guys around?
Not their specialty but if they can repair regular stuff, have test instruments and tools, etc., maybe one can be guided to repair an unfamiliar (to him) Guitar amp.

Tube amps are relatively "easy": circuits are classic, "everything is visible", they are relatively robust, meaning a tube can stand a short or lack of bias (for a few seconds enough to notice) while SS amps can die in milliseconds and damage a lot of direct coupled parts.
Just a suggestion.

Yep. 3 hours either way to an amp technician. Oh the joy of living in a mountain ski town :)
I am fairly competent with a multimeter. Most importantly I know how to be careful around electricity, especially when I am not sure. I will pop the chassis out this weekend and hopefully withbyour guys' pointers, get in the direction I need. I am also going to order a set of new tubes!
 




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