Please help me out. 1969 100w build

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Tazin
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Re: Please help me out. 1969 100w build

Post by Tazin » Sun Jun 03, 2018 4:43 pm

You gotta love this amp...It's the ole "two steps forward one step back"! Anyhow, I agree that the rest of the voltages look pretty good now with exception of the missing bias voltage at the output tubes. So, at the White bias wire where it connects to the turret board (at the 27K resistor) you have 99 volts ac. Check the dc voltage at the output of the bias diode (junction of the diode and the 15K resistor). If you've got dc voltage there then double check the Black ground wire & the buss wire that connects the one end of the bias caps & trimmer pot to ensure it has a good connection at all points. You can also try turning the trimmer pot a little to see if you can get a dc voltage reading at Pin #5 on the output tube sockets.

The testing/measuring conditions should be the same as when you did the voltage chart.

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neikeel
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Re: Please help me out. 1969 100w build

Post by neikeel » Sun Jun 03, 2018 4:43 pm

no0sand1s wrote:
Sun Jun 03, 2018 2:47 pm
the metro assembly instructions stated to leave the standby 'off', so it was never on during my previous voltage readings.

here's a link to voltage chart results: https://www.flickr.com/gp/wedinbordeaux/V49ipa

everything looks great, except I lost -50 V @ pin 5 of each output tube location. I checked the bias wire voltage where connected to the turret board and read 99 VAC.
:popcorn:

So if you have 99vac on the feed, and you had correct before - follow the voltage after the 27k (still ac) after the diode dc and from there after the 15k and then to the junction of 15k and second bias cap to the junction of the 220k resistors and then to pin 5s
See where the voltage goes AWOL.
Neil

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Tue Jun 05, 2018 6:21 pm

All good now!! I had a bad connection at the diode connected to the 27K resistor. I'm going for the power tubes and will follow up with you. Thanks for holding my hand through this!

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Tue Jun 05, 2018 11:37 pm

Hello gentlemen. Please check out my PPIMV mod, if you would. I want to make sure I wired everything correctly before firing up. I also enclosed a sound clip prior to the mod - I haven't played in 20+ years. Sounds great!
https://www.flickr.com/gp/wedinbordeaux/88y25V

Let me know if you're ever in Chicago...

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neikeel
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Re: Please help me out. 1969 100w build

Post by neikeel » Wed Jun 06, 2018 4:49 am

:shred: :toast:
Neil

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Wed Jun 06, 2018 7:50 am

Can I assume that means my modification is correct?

I can’t thank you guys enough for helping me out.

Tazin
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Re: Please help me out. 1969 100w build

Post by Tazin » Wed Jun 06, 2018 3:42 pm

I see you got the amp going. Is that the Ken Fisher "Type 2" master volume? What did you bias the amp to?

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Wed Jun 06, 2018 3:54 pm

Metroamp mod - also called Rich Mod PPIMV II. I biased to 38mv.

https://web.archive.org/web/20130224052 ... y_Step.pdf

Tazin
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Re: Please help me out. 1969 100w build

Post by Tazin » Wed Jun 06, 2018 4:31 pm

I believe the Rich Mod PPIMV II is very similar to the Fisher "Type 2" MV...The Fisher uses a different pot value though.

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neikeel
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Re: Please help me out. 1969 100w build

Post by neikeel » Thu Jun 07, 2018 4:57 am

Although the LArmar has lots of fans I am pretty sure George still uses this one with a dual 500 PEC pot?
Neil

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Thu Jun 07, 2018 10:21 am

Yes, that’s correct. Could you please take a look at my wiring and see that it is correct? Thank you

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neikeel
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Re: Please help me out. 1969 100w build

Post by neikeel » Thu Jun 07, 2018 5:35 pm

It is impossible to tell from the close ups.
But as long as the wires match up it looks ok

What is your plate voltage (vs bias current)

Assuming 490v on plates 17.5/490 = 36mA so you would be a bit too hot.

If you have 460v on plates 17.5/460 = 38mA

Depends on how you are biasing (1 ohm resistors vs bias probe)

Sorry cant see voltage chart any more but personally I would back it off a bit whilst it beds in, maybe 30-32mA tops
Neil

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Thu Jun 07, 2018 11:19 pm

I'm SOL again. :what:

Take a look at the new voltage chart. Output tubes were removed, and I reset bias to 50 volts.
https://www.flickr.com/gp/wedinbordeaux/655VM2

During the process (while noting voltages on V4), bias voltage on pin 5 of V4, 5, 6, and 7 disappeared. 3.4 volts for the heaters disappeared across all tubes. I powered off/ on again and those voltages reappeared. Bad PT?

Regarding the PPIMV - all wiring connections from the pots are correct - my close ups were provided to check on the connection of the wires to the turret board and for the terminal strip connections. Please check those out.

Thanks
Stephen

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neikeel
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Re: Please help me out. 1969 100w build

Post by neikeel » Fri Jun 08, 2018 2:40 am

Did a probe slip and you blow a fuse?

check your heater connections to v7.

Personally I would have run it a bit more before modding but I guess a ppimv or good attenuator is the only way of running a 100w nowadays

Your bias is now connected via two grid stoppers (220k). Check those connections. The signal reaching those grids is adjusted via the two pots.
Neil

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Fri Jun 08, 2018 7:57 am

Both fuses are fine. While obtaining voltage readings yesterday, heater voltage reappeared across all tubes after turning the power off and then back on.

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