68 plexi

[lautmaschine]

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

[julkke]

I'd bet it's a 820.

[neikeel]

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.

[julkke]

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.

[Maverick]

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

[julkke]

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

and...?

[gloeidraad]

I think a big bright cap(5000pf)?

Erik

[neikeel]

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

[gloeidraad]

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.

Erik

[neikeel]

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.

Erik

We agree! A few others do not.............

[RockinRocket]

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?

[Tazin]

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.

[whopperplate]

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

[RockinRocket]

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

[whopperplate]

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