'68/69 50W Tremolo project

[sonicmojo]

Certainly looks like the Metroamp circuit is way more robust with trimpots to tune and actually uses both triodes. I hope I don't have to redesign to that but we'll see.

Martin, I also thought the connecting cap was a .1 uF.

Thanks. Will post progress soon.

[Reeltarded]

.01u!

Here is it.. ignore 330u cathode usually 250 there.


M

[martin manning]

1959T: https://drive.google.com/drive/folders/ ... lpLclBqSDA

0.1u!

[imusbnutz]

Hey all. Long time member/lurker. First time poster. I wound up here today while searching Google. I was looking for chassis dimensions of the early Model 1962 Bluesbreaker with Trem and GZ34. I’m considering a build for a 2x12 32in W x 23in H x 10.5in D combo cab. Sure can’t afford to buy one. Point is, I've collected some info in the last few days that might be useful here.

First, I’m no Marshall expert but my unsolicited advice is to proceed carefully as this amp is likely to only become more valuable with time. I’m 99+% certain this amp is late ’66 to ’67. The iron, tube and power filter caps locations are all factory installed. The tube rectifier is not a user mod. My guess is being a Model 1961 4 x 10in makes it more rare than the 2 x 12in.

Search Ebay for "Vintage 1967 Marshall JMP Bluesbreaker Tremolo 50". You'll find plenty of hi-res images including gut shots. Serial is #10043 (within 84 of the amp discussed here.) I did notice the original green input wires have been clipped and replaced with shielded cable to the first preamp tube. It also has some box caps installed down on the tremolo end of the circuit board. Obvious things. After 50 years there are likely other mods to be found. The asking price is US $14+ thousand with 28 watchers. The seller is taking Offers so who knows?

Here is a link to a very fine example of a slightly different and earlier Bluesbreaker that sold on Reverb for $21,210.34 + $213.17 Shipping within the last 2 years.
reverb.com/item/884179-66-marshall-jtm45-bluesbreaker-mk-iv-model-1962-2x12-tremolo

If you don’t mind sharing, what is the number of the transistor. I can’t seem to find a legible schematic. Looks to be PNP germanium and is likely not that critical.

Either way, hope the links help and best wishes.

[martin manning]

If you don’t mind sharing, what is the number of the transistor. I can’t seem to find a legible schematic. Looks to be PNP germanium and is likely not that critical.

Should be 2G374 PNP BJT. Maybe Bryan can get a read on what is in this amp.

[Reeltarded]

Yep, don't be amazed. An early supernice never gigged Bb combo with the early knobs and right logo sell for around 12-14k. The rest honestly have no hope near that. The 4x10 is rarer, and nobody cares except for about 10 people who already own three... gotta be careful about chatting up what a listing makes values appear to be. There is hardly a market for much at all these days. Most things you see at fantastical prices have been listed the same for ten years and it never worked out.

This year, 10 collectors for life are going to die and they are going to flood the market with 5000 pieces that have been in the dark of their private collections for 30 years. Next year; 12.. when mint stuff comes up it goes for money. Anything tampered with in the slightest lingers forever at retail plus 60%.

That's the reality.

[sonicmojo]

Here is a pic. Looks to be an NTE 102A which I think is a compatible replacement. The good news is that it works for the amp as I have the tremolo operable again after hooking things back up. The amp currently has incorrect value pots for Intensity/Speed so I will replace them with 50K/2M to get it back to stock.

[sonicmojo]

Search Ebay for "Vintage 1967 Marshall JMP Bluesbreaker Tremolo 50".

Thanks for this eBay one. It does look like the same board materials as the one I've got.

[sonicmojo]

1959T: https://drive.google.com/drive/folders/ ... lpLclBqSDA

0.1u!

Thanks Martin, this is exactly what I used to get it back to working in single triode. This amp still had the 680k resistor and most of the same other values. I had to move a couple of things and add a couple of resistors on the pots but basically all the under board connections and wires were still there for this layout except the tube placement was different. I got messed up for a bit as the heater pin on the trem socket was missing and I hooked up the heater to pin8 until I realized it was missing. Helps to count! I pulled a pin from a different socket and put it back in the original without removing the socket. It worked out luckily.

[martin manning]

Smooth move on the socket pin. How does it sound?

[sonicmojo]

Smooth move on the socket pin. How does it sound?

It is still on my bench and I've been distracted this weekend so I hope to get it tuned up soon and will report back!

[Reeltarded]

I found one pick of the last combo I had sold and it's identical but the 2x12 brit domestic model with a step up transfomer. I wish I had that amp back.. so I could sell it again. heh

[sonicmojo]

So the weird thing about the cab is that one of the 10" non-original speakers had been modified to be a few degrees off center with a new mounting hole so the one closest KT66 would not hit the basket. Would any of the 1961 4x10s in this style cabinet have come with KT66 stock? The tube was literally in the basket a few millimeters from the cone. The owner of the amp had some more period correct speakers that I put in it that would have the same problem with KT66s so I'm going to use EL34s instead.

[Reeltarded]

KT66 not original to that amp. Another attempt to JTM45 it.

[sonicmojo]

Finally fired it up with some EL34s. Hard wired bias is actually not too far off where I would like it, I may add a small internal bias pot. With the KT66s that were in it, it was too hot so I think whoever had this last may not have changed bias for those tubes. I had to spend quite a bit of time with tiny rolled up sandpaper on the power tube sockets to clean them to working condition.

It sounds pretty good! Everything seems to function pretty well except the tremolo, LOL... Right now the intensity sweep is between 8.5-10 and goes from nothing to thumping and very cut volume almost instantaneously. Hopefully correct value pots and a bit of tweaking will bring that to more a useful state. One of the plastic speaker jacks broke, ugh. Will have to replace that too. It's a player!