Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Toxophilite on February 24, 2015, 12:35:32 am

Title: Pop goes the weasel!
Post by: Toxophilite on February 24, 2015, 12:35:32 am: Maybe I'll splurge on a fancy can cap after all....

(this I believe was a result of a bad rectifier I tried by accident)
Title: Re: Pop goes the weasel!
Post by: Willabe on February 24, 2015, 09:22:46 am: You OK? :w2:
Title: Re: Pop goes the weasel!
Post by: sluckey on February 24, 2015, 09:30:11 am: A bad rectifier could possibly damage the choke and the second filter cap as well. May want to check those too. In fact, check all your filter caps.
Title: Re: Pop goes the weasel!
Post by: Toxophilite on February 24, 2015, 10:17:21 pm: I'm okay
It was a bit of a fright but more just startling
I have a box of 5U4GBs and the one I had in the amp looked like's it's getter flash was getting pretty small so I put this other one in which looked a lot better
The amp came on and was dead quiet, so i switched the standby on and off(it's on the back I thought I had forgotten to turn it on), Nothing , and then a second or too later 'BANG!!' and smoke poured out of every crack and crevice in the chassis...it looked kind of cool in objective my-amp-is-blowing-up sort of way
Needless to say the power section was filled with 'cap-fetti'

I replaced the cap that blew and tested the rectifier which read 'bad' (mind you it could've been killed!)

I then cautiously tried another tested rectifier and in putting it in i noticed the rectifier was quite wiggly in the socket, so I tightened the pins a little, still wiggly, maybe a little better

i turned it on and he amp came on, and then went off, and then on, and then off, cycling consistently from one to the other. I tested the voltage at 'A' (right after the rectifier) and it was going up and down, up and down!! Soooo I turned it off to ponder

The choke has a DC resistance of 471 ohms (out of circuit)
i haven't tested anything else yet

I kind of wish I had a camera handy right after it blew!!
Title: Re: Pop goes the weasel!
Post by: Toxophilite on February 24, 2015, 11:23:55 pm: I noticed ground lead the 10 uf cap parallel to the exploded one had come disconnected (broken ^%$&^%$ solid wire!)
Probably went I was trying different dropping resistors in the power supply
I put in a couple of 10uf in parallel to replace it (total 42 now) and a tested rectifier and it works again though there's a little hum now annnd the voltage is slightly higher 390 vdc coming off the rectifier 386 at 'B' going to the power tubes
And the ma measurement at the cathode resistor is now 28ma which is a little high yes?
might have to install the adjustable bias circuit
Title: Re: Pop goes the weasel!
Post by: Toxophilite on February 25, 2015, 02:31:44 am: Discovered another likely link in the chain of cap disaster.
A rectifier with a MISSING guide pin..
:cussing:
A fellow I know just tosses octal tubes with missing guide pins in the garbage..I can see why now!
Title: Re: Pop goes the weasel!
Post by: sluckey on February 25, 2015, 06:55:44 am: https://www.tubesandmore.com/products/P-STKY-1 (https://www.tubesandmore.com/products/P-STKY-1)
Title: Re: Pop goes the weasel!
Post by: Toxophilite on February 25, 2015, 12:37:00 pm: Hey that's a good idea
I have a a few duds in my batch of rectifiers (I tested them all the other day)
I'm going to cut the bottom off of one (after disposing of the glass of course!)
Title: Re: Pop goes the weasel!
Post by: shooter on February 25, 2015, 01:51:06 pm: I've taken dudes, drilled a hole in the bottom to fit an LED, they make good, albeit fragile, panel lights.
Title: Re: Pop goes the weasel!
Post by: lego4040 on February 25, 2015, 03:42:29 pm: I had one go like that years ago on a Vintage BoomBox rebuild, I put Cap back in Backwards. Yeah I almost pissed my pants