First post... long time lurker (and learner of things from you guys).
Built my second amp from a kit from RJ. Got a liverpool kit with Pacific transformers. Great guy to deal with by the way. Anyway, wired up my liverpool and flipped on the power, tubes heat up, power light comes on, then I switch on the standby after a minute of two. Nothing, nada, no sound. Just a foul fishy odor coming from my transformer. Turned it off immediately but alas... RIP OT. From what I have read, that's a good indicator of a blown tranny. I also measured the resistance of the plates on the output tubes from the B+ wiring with a DMM and got like 2.7M readings. Which I also read was a good indicator of a blown tranny if it reads over 1K. http://www.geofex.com/ampdbug/outtrans.htm
Guess I'll be picking up another. Dammit!
Went over my wiring through and through and all I can come up with is possibly wiring up the impedance rotary selector wrong.... costly mistake. Live and learn. Ordering a new one.
(BTW... my first build was a DR Z Carmen Ghia which turned out awesome.)
Mismatched impedance leads to power tubes failure first,then maybe a fuse,and after long overheat the ot goes down.
More probably a defective construction or material.
Inviato dal mio Moto G (5) Plus utilizzando Tapatalk
Thanks for the replies fellas. I don't have any completed pics to post but I'm under the impression that it was probably a dud OT. The smell was awful. It reeked like fish.
I think it would be better if I replaced the OT with a new one than to risk damage to other components.
I emailed RJ and he said the test I did would confirm a bad OT.
frankdrebin wrote: ↑Sat Sep 01, 2018 12:37 pm
Mismatched impedance leads to power tubes failure first,then maybe a fuse,and after long overheat the ot goes down.
More probably a defective construction or material.
Inviato dal mio Moto G (5) Plus utilizzando Tapatalk
I was surprised a fuse or tube didn't blow either which makes me think maybe you're on point here.
I wouldn't have thought it'd have blown that quickly?! Check all your wiring first.
I would expected the valves to red plate unless the plates connection was grounded. I would look at what went wrong and at least have a small fuse in the centre tap of the output transformer to prevent blowing another output transformer something a bit over 100mA should be fine. Removing it when the amp is found to be working fine.
A reversed electro cap will explode given the right conditions. A builders REALLY needs to check the electrolytic caps before flicking the switch. It could be costly as well as dangerous.
Mark wrote: ↑Sun Sep 02, 2018 1:45 am
A reversed electro cap will explode given the right conditions. A builders REALLY needs to check the electrolytic caps before flicking the switch. It could be costly as well as dangerous.
I couldn't agree more. This wasn't a electrolytic cap though. Just a bad OT out of the box.
Littlewyan wrote: ↑Sun Sep 02, 2018 4:37 pm
As long as you're sure mate, don't want anything else getting damaged. You should build yourself a light bulb current limiter.
good point. I saw the plans for one around here, but I never got around to building one. Will probably do so as I already started my 3rd build (JTM45) while waiting on new OT.
Also going back over my wiring I did find a wire that I missed soldering from the presence pot to C11/R11. The wire was there but wasn't soldered in. I'll bet that had a hand in this debacle.
Got a new OT coming soon. Looking forward to getting this thing up and going. I will definitely take precautions and check and double check everything before flipping the switch this time.
if it failed and you were not playing you either had something wired up wrong on the primary side or the OT was faulty out of the box, it happens.
When you are not playing there is almost no current on the secondary of the OT, just hiss and any hum, so a miss-wiring there would do nothing on initial start up. (caveat if you have negative feedback and it is connected the wrong way around it could squeal on startup, but you would hear the lamination's vibrating if that was the case.)
