Ok, another issue for which I could graciously use some help. I thought it would be easier just to start a new thread.
Initially I started up the amp with 6v6s without any problems with a bulb limiter. I got some EL34s today. For some reason, something in my head kept saying to plug in the bulb limiter again before trying the new tubes. Go figure, when I put in the EL34s and flipped the switch, the bulb went bright and wouldn't dim down at all. Quickly turned it off.
I pulled the EL34s and the bulb limiter dims as expected. Put in the 6v6s, bulb limiter dims as expected. Put in one EL34 in either socket and the bulb limiter lights up bright.
Looking closer at the differences between the two types of tubes, the 6v6 is missing pins 5 and 8; EL34 is missing only pin 5. Something's up with pin 8 and my build. Pin 8 is nothing but a ground. So what's going on here?
First...you're looking at the pins 'backwards'. Both tubes have both pins 5 and 8...5 is the main input grid on both and 8 is the cathode on both.
The EL34 is not using pin 6 and the 6V6 doesn't use pins 1 and 6.
In an EL34, pin 1 is the Suppressor grid and is usually connected straight to ground (or the cathode). The 6V6 actually has this connection inside the tube (and it's not actually a suppressor grid but rather beam forming plates).
This is a very helpful site...bookmark it...you'll be back!
When looking at the socket from inside the amp...start at the gap and go clockwise...starting at pin 1. If you look at the socket from the other side it's reversed. Looking at the socket from inside the amp is the same as looking at the tube base.
Thanks Fischerman. My bad....as usual. So pin one could be the culprit? It's simply connected to ground, connected to pin 3 via the diode train, and connect to pin 8 via a jumper wire.
Fischerman wrote:That sounds right so I dunno why that would happen. Pics are often very helpful so if you have the means you might want to take a few and post them.
Being at work I'm limited to just a few pictures. Here's one that I enlarged a little. I don't know if it'll help though.
Ron,
This is what I would do, someone else might have a better suggestion but this seems logical to me.
I would inspect the amp thoroughly. I know, you have been there several times already.
Pull all tubes including preamp tubes and fire it up.
Install tubes one at a time and see if you can get back to a working amp with 6v6s (like you originally had). Maybe its actually a bad preamp tube, filter cap or wiring. The importatnt thing is to do one thing at a time so you can pinpoint an area if things go south.
If you get to the point of a working amp with 6v6s. Compare present voltages with your original voltages. If that checks out, I would question your EL34s.
Seems long winded but at this point it would make sense to me to start at the beginning.
Hm. You know whats weird about your photo? The pin guide should be visable right at the base of pins 1 & 8 - I don't see it. Is this photo really that bad or is something really backwards?
Most people stall out when fixing a mistake that they've made. Why?
rooster wrote:Hm. You know whats weird about your photo? The pin guide should be visable right at the base of pins 1 & 8 - I don't see it. Is this photo really that bad or is something really backwards?
I've got up and running with 6v6s no problem. Been playing it for about hour. Sounds great. Tried the EL34s again, but the bulb limiter lit up brightly.
Here's a closeup. You can clearly see label 1, 2 and 8. You can see the diodes connected accordingly:
OK, I can see the numbers clearly. Hmm, never heard of such a thing. Have you tried this set of tubes (E34Ls) in a different amp and do they actually work? The worst you have to lose is a fuse - if you have the OT fused. Do you? You could lift the B+ to the OT and temporarily fuse it with a .5A fuse.
For that matter, do you have another set of EL34s?
Most people stall out when fixing a mistake that they've made. Why?
You guys are so smart. It was, IN DEED, a bad tube. A friend came over last night with a set of SED EL34s, and worked great. I apologize for the fire drill. Being new to the amp building world is stressful at times.
Ok, this amp is an absolute monster. It can go from lean to mean better than anything I've played or heard to date. It's articulate, flamboyant, refuses to let a note die. Puts a huge smile on my face. I never thought that an amp of this quality could be had for about $400-$500 worth of parts and some sweat. Awesome.
Ok, I've got the bug now. What should I build next? hmmm
This forum and it's community is truly incredible and supportive. Thank you.
Fischerman wrote:My apologies then and you learned rule #1 when troubleshooting a tube amp: ALWAYS suspect tubes first. I just assumed you had.
No worries. I only had one pair of tubes at the time (brand new set of JJs). Go figure. I really didn't expect the tubes to be bad. Won't make that assumption again of new tubes.
Is this photo really that bad or is something really backwards?
