50W head - 1976 I think?

[nobbydog]

So I'm borrowing this from a friend for a few gigs, the signed sticker inside dates it 20/8/76, so I guess that that, but I cant seem to find any other examples of this 'LEAD & BASS 50' head. Is it a variant of the 1983 series, and does the serial number throw up any more information or guide ti its history? The S/N is 0992H. Thanks and apologies if this has been posted before, but I cannot find a definitive guide to old serial numbers etc anywhere.

 

[Pete Farrington]

Maybe a model #1964?
There’s a mention of it https://www.drtube.com/marshall-jmp/

JMP 1964 Lead and Bass, 50W Head​

This amp was in production from 1973 up to 1976. This is a two channel amp, one channel is that of a 1987 Lead amp and the other channel is that of a 1986 Bass amp, making it quite a versatile amp. The 2100 is the combo version of this 1964 head.

But no actual schematic.

A friend had the earlier lead and bass model #1962 combo.

 

[TonyK]

That sounds/looks right. My first valve amp in 1974 was a really beat up Selmer Treble & Bass and I replaced it with a Marshall Lead & Bass 50W head with a 4x12 slant cab in 1976. It was way too loud for any of my needs and my group was a club/pub-based variety group, with a little rock thrown in (Deep Purple, Black Sabbath, Free etc.) except that I could never find that great tone I was looking for, even with my SG (which I still have) - no one told me that I had to turn it up! Way before internet lol. Unfortunately I moved to the States and never replaced it due to "real" work and a family getting in the way. I really miss that rig. Good luck with it and post back with the results you get!

 

[Thepartyprogram]

Easy to turn these into a "lead" version... last of the flip switches before goin Rocker switch?

 

[JohnW]

I have the exact same head with the same master volume mod. Same year too.

 

[timsmcm]

yes that is the stuff. I would not do a thing to it but check the caps and if not leaking or swollen turn it on standby and let it sit for a while. Then turn it to 10 and get after it. Great amp.

 

[Pete Farrington]

The stock standby arrangement on 70s 50 watters is a joke, comedically awful, as it applies HT to hot valves before the bias supply has charged up. Hopefully most have been modded to a more sensible arrangement by now, but valve killer unmodded examples still turn up here.

The bias supply feed needs to be on the hot (unswitched) side of the standby switch, so as to allow the bias supply to charge up whilst in standby.

 

[Derrick111]

The stock standby arrangement on 70s 50 watters is a joke, comedically awful, as it applies HT to hot valves before the bias supply has charged up. Hopefully most have been modded to a more sensible arrangement by now, but valve killer unmodded examples still turn up here.

The bias supply feed needs to be on the hot (unswitched) side of the standby switch, so as to allow the bias supply to charge up whilst in standby.

I think that mostly applies to pre 1973 50 watt Marshalls. They seemed to have moved the bias supply to the proper side of the standby switch by 1972 or 1973. Marshall also started installing screen resistors on the output tubes around the same time on 50 watters.

 

[pulsonicsound]

Great amps!

I have two of these as I like them so much!

The combo version is also very cool!

 

[Pete Farrington]

I think that mostly applies to pre 1973 50 watt Marshalls. They seemed to have moved the bias supply to the proper side of the standby switch by 1972 or 1973…

Dunno, I recall seeing the hara-kiri standby in late 70s JMP 50 watters, the schematics seem to support that https://el34world.com/charts/Schematics/files/Marshall/Marshall_50w_master_vol_2204.pdf

https://www.drtube.com/schematics/marshall/78331-2.gif

 

[Derrick111]

Dunno, I recall seeing the hara-kiri standby in late 70s JMP 50 watters, the schematics seem to support that https://el34world.com/charts/Schematics/files/Marshall/Marshall_50w_master_vol_2204.pdf

https://www.drtube.com/schematics/marshall/78331-2.gif

Weird... I have not needed to modify a single one from '73 on and I've had/worked on quite a few. That white bias voltage supply wire on the block rectifier moved before the changed to PC, and that was in mid/late 1973. That move put it on the correct side of the standby switch. You also see a lot less 50W Marshalls with replaced power transformers after 1972 as a result. Quite easy to confirm with a multimeter.