YMI5150? 12003 build

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Re: YMI5150? 12003 build

Post by Strat78 » Tue Jul 17, 2012 12:23 am

The bias caps are jumpered under the pot?
Last edited by Strat78 on Mon Feb 11, 2013 2:26 pm, edited 2 times in total.

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Re: YMI5150? 12003 build

Post by vh junkie » Tue Jul 17, 2012 6:36 am

The pot back (center wiper) should connect the two caps. I cannot see the 15k resistor on the across the other end of the caps.
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Re: YMI5150? 12003 build

Post by axeman » Tue Jul 17, 2012 8:39 am

Grounded?

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Re: YMI5150? 12003 build

Post by YMI5150? » Tue Jul 17, 2012 9:30 pm

axeman wrote:Grounded?
nope. missed one. all set now.

HP is on loan until Friday but the amp is functional. amazing how loud it is, even on zero and how much pick attack affects tone.

One issue is my tubes are pretty severely mismatched. all fat bottles. bias current is about 40, 34, 20, 5. suggestions on values when buying a replacement? I'll probably buy a pair and find the best 4.

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Re: YMI5150? 12003 build

Post by YMI5150? » Wed Jul 18, 2012 7:42 pm

Until I get some more tubes, does it make sense to balance biased tubes in pairs so the total is similar on both sides? Say highest and lowest on 4 and 5, and middles on 6 and 7.

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Re: YMI5150? 12003 build

Post by Strat78 » Wed Jul 18, 2012 10:32 pm

Highest at 4 and 7, lowest at 5 and 6. Are those EH tubes? Los Gatos and Saratoga is a nice part of the bay area. That whole south bay area used to be the best "stone fruit" region in the world, what now is silicon valley. You can probably grow avocados in your back yard or even pygmy bananas against the south facing wall of your house! I think I'm missing California. :cry:

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Re: YMI5150? 12003 build

Post by axeman » Thu Jul 19, 2012 1:34 am

YMI5150? wrote:
axeman wrote:Grounded?
nope. missed one. all set now.

HP is on loan until Friday but the amp is functional. amazing how loud it is, even on zero and how much pick attack affects tone.

One issue is my tubes are pretty severely mismatched. all fat bottles. bias current is about 40, 34, 20, 5. suggestions on values when buying a replacement? I'll probably buy a pair and find the best 4.
The tube thats reading 5 is no good so is the 20 maybe.

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Re: YMI5150? 12003 build

Post by vanhalen5150 » Thu Jul 19, 2012 7:08 am

You have a tube thats reading 5?
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Re: YMI5150? 12003 build

Post by YMI5150? » Fri Jul 20, 2012 12:51 am

These are all vintage tubes. 2 sylvanias and 2 RCAs from roger. Had a weird hum this morning so I shut it down.

Tonight I threw in the quad of EL34s from my original kit and it was fine. Interesting, when pot was dialed way back these measured 10-15. So the 5 is not way off. It's more like I have 2 very hot fat bottles.

I may just grab a quad of EHs and call it a day...

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Re: YMI5150? 12003 build

Post by rgorke » Fri Jul 20, 2012 4:49 pm

Maybe try just with the two I sent you in 5/6 or 4/7?
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Re: YMI5150? 12003 build

Post by rgorke » Fri Jul 20, 2012 4:50 pm

vanhalen5150 wrote:You have a tube thats reading 5?
I have a bunch that read all over the map. I have a different resistor in my amp to bias with a lower voltage. The tubes range from 22 down to 2.9.
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Re: YMI5150? 12003 build

Post by YMI5150? » Fri Jul 20, 2012 6:02 pm

Oh boy, I smell another variable...

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Re: YMI5150? 12003 build

Post by YMI5150? » Mon Aug 06, 2012 1:13 am

I had the house to myself for once and about 2 hours in, I was wearing my headphones listening to my rig mic'd and all the sudden i lost sound. looked over and the indicator light was out. no abrupt pop but a pretty nasty melted plastic smell. I shut her down. tubes seemed fine. PT was exceptionally hot. OT was very warm. blew the main fuse. first time I've ever popped a fuse. dont recall hitting a massive power cord. just gave up on me.
thoughts before I power it back up?

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Re: YMI5150? 12003 build

Post by vanhalen5150 » Mon Aug 06, 2012 7:47 am

Did it just suddenly quit, or did it die out? I'm thinking you blew the PT. Do you have voltage at the F1 can cap?
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Re: YMI5150? 12003 build

Post by YMI5150? » Mon Aug 06, 2012 10:04 am

no B+ voltage and it stinks when i turn it on. fuse didnt blow. the bigger question is why did it happen? amp was heavily attenuated, say -16 or more dBs for two 1 hour stints, running at 95 volts. I've run amps like this before with no trouble.

need to find root cause.

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