68 plexi

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lautmaschine
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Re: 68 plexi

Post by lautmaschine » Wed Dec 05, 2012 5:08 pm

Was anyone able to determine if the v1b resistor is 2k7?

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Re: 68 plexi

Post by julkke » Wed Dec 05, 2012 5:41 pm

I'd bet it's a 820. ;)

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Re: 68 plexi

Post by neikeel » Thu Dec 06, 2012 5:43 am

julkke wrote:I'd bet it's a 820. ;)
+1

An 820 cn be a bit gritty with humbuckers and give a bit of fizz (not a problem with the tones here) if trying to play cleanly but a 1k5 is a compromise between that the 2k7.
Neil

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Re: 68 plexi

Post by julkke » Thu Dec 06, 2012 6:48 am

neikeel wrote:
julkke wrote:I'd bet it's a 820. ;)
+1

An 820 cn be a bit gritty with humbuckers and give a bit of fizz (not a problem with the tones here) if trying to play cleanly but a 1k5 is a compromise between that the 2k7.
I gotta try that 1.5k because I can't decide which do I like better, 2k7 or 820r.

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Re: 68 plexi

Post by Maverick » Sat Dec 15, 2012 9:30 am

I have figured out why some of those 50watt 1987 series amp gain up so quick
Akme Guitars

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Re: 68 plexi

Post by julkke » Sat Dec 15, 2012 9:38 am

Maverick wrote:I have figured out why some of those 50watt 1987 series amp gain up so quick
and...?

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Re: 68 plexi

Post by gloeidraad » Sat Dec 15, 2012 9:48 am

I think a big bright cap(5000pf)?

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neikeel
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Re: 68 plexi

Post by neikeel » Sun Dec 16, 2012 3:17 pm

:palm:

Seem to remember mentioning that one or twice before, a big bypass cap on the pot is not a 'bright cap'!!
Neil

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Re: 68 plexi

Post by gloeidraad » Sun Dec 16, 2012 4:03 pm

I agree with you,but it is one of the reasons that they are a bit gainy at lower volume settings.
It is more of a bandpass depending of where the potmeter setting is. :peace:

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Re: 68 plexi

Post by neikeel » Mon Dec 17, 2012 3:45 am

gloeidraad wrote:I agree with you,but it is one of the reasons that they are a bit gainy at lower volume settings.
It is more of a bandpass depending of where the potmeter setting is. :peace:

Erik
We agree! A few others do not............. :what:
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Re: 68 plexi

Post by RockinRocket » Mon Jun 27, 2016 7:45 pm

Old thread that wooperplate linked.

Did the plate volts get determined? Im betting their low.

Also I wonder what the cathode follower resistor is. It would be easy to mistake a 10k as a 100k. That could add some compression.

What was the feedback resistor connected to?

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Re: 68 plexi

Post by Tazin » Tue Jun 28, 2016 9:25 am

The Drake 1202-118 PT's were fairly consistant voltage wise so I would venture to say the plate voltage was normal.

I've seen a fare share of anomalies in the Marshall circuit but a 10K resistor in place of a 100K for the cathode follower isn't one of them.

The nfb is taken from the output solder terminal on the Selector as opposed to a particular secondary tap.

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Re: 68 plex

Post by whopperplate » Sun Jul 03, 2016 11:38 pm

I was looking at an old thread talking about how transitional amps from this era are often wired incorrectly on the b+ line with the last 10k dropping resistor wired out of the circuit essentially.

viewtopic.php?f=16&t=44511&hilit=50k+mid+pot&start=15

All of the links to uploaded photos showing examples are non existent. With This amp being from that era and also having the 10k oriented on the board in a way I have only seen common In this era amp I assume that this may be suspect as well. Any knowledge?

Thanks

Charlie
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Re: 68 plexi

Post by RockinRocket » Mon Jul 04, 2016 8:35 am

As someone else mentioned I bet those CC 10ks have drifted well out of spec.

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Re: 68 plexi

Post by whopperplate » Mon Jul 04, 2016 1:30 pm

Those are both 8k2 in this amp, and I am referring to the 10k Iskra terminating near the potentiometers by the dual .022uf mustards. Apparently, according to Tazin in the linked thread I provided, the transition lamps of this period often wired this incorrectly.

Charlie
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