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Post by De ville on May 7, 2021 23:26:40 GMT -5
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pdf64
Wholenote
Posts: 556
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Post by pdf64 on May 8, 2021 3:36:23 GMT -5
It looks bigger than I’d expect but I think that there were 3 different PTs for the 50W models in the 70s, so it’s hard to be certain.
Note that the earlier 4 hole JMP 2204 doesn’t have the same degree of cascading preamp gain as the JCM800 era model.
And the JMP 50W models have an awful standby which sucks the life out of the output valves, just need to move one wire to fix it.
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Post by Leftee on May 8, 2021 11:24:37 GMT -5
It’d be good to get better pics. Is that possible.
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Post by De ville on May 8, 2021 22:12:52 GMT -5
I asked the seller for better photos.
pdf64, great info.
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Post by Leftee on May 9, 2021 8:53:39 GMT -5
From the images they look the like the same transformers that are in my ‘76 4-holer.
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Post by De ville on May 9, 2021 21:15:48 GMT -5
Well it looks sloppy in there, and my guess is modded. Did the amp come from a combo, the label says combo. |
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Post by De ville on May 9, 2021 21:16:48 GMT -5
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Post by De ville on May 9, 2021 21:18:38 GMT -5
Apparently the seller doesn't know what transformers are. He didn't send transformer photos. I'll explain it to him.
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pdf64
Wholenote
Posts: 556
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Post by pdf64 on May 10, 2021 11:51:46 GMT -5
... Note that the earlier 4 hole JMP 2204 doesn’t have the same degree of cascading preamp gain as the JCM800 era model... Oops, sorry the JMP 2204 only has 2 input jacks, not 4. drtube.com/schematics/marshall/2204u.gifThose photos aren’t super helpful, but I get the impression that it’s been modded to the JCM style cascading inputs, so should have a reasonable degree of preamp overdrive available, if wanted. And it looks like the bias supply has been modded, so standby should be ok to use. |
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Post by De ville on May 10, 2021 19:24:57 GMT -5
Ya, the photos are not the best. LOL. I have some more.  |
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Post by De ville on May 10, 2021 19:26:27 GMT -5
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Post by De ville on May 10, 2021 19:27:09 GMT -5
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Post by De ville on May 10, 2021 19:27:52 GMT -5
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Post by De ville on May 10, 2021 19:28:48 GMT -5
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Post by De ville on May 10, 2021 19:33:56 GMT -5
I think the transformers look correct.
Anyone see anything of concern?
Correct me if I'm wrong, but shouldn't the last tech have cleaned up the flux?
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Post by Leftee on May 10, 2021 19:41:56 GMT -5
Your PT looks correct. It’s a Drake 1202164.
That much I know.
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Post by Leftee on May 10, 2021 19:45:20 GMT -5
I think the choke is right, as well (also a Drake). I didn’t recall the label, though.
I’ll go out on a limb and say the OPT is original too.
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Post by De ville on May 10, 2021 20:48:36 GMT -5
Yes, I think I see a date ink stamp of 9/77, and the amp is a 1977.
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Post by Leftee on May 11, 2021 6:41:09 GMT -5
I see it’s been converted to EL34s too. 👍
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Post by De ville on May 11, 2021 13:44:49 GMT -5
Thanks for pointing that out. It sounds like that's a popular mod. Supposedly this amp was last worked on by Andy Marshall, designer of the THD hot plate.
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Post by Leftee on May 11, 2021 19:10:29 GMT -5
I believe it would have shipped with 6550s. Not exactly sure of that timeline, though.
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Post by De ville on May 11, 2021 20:52:18 GMT -5
That should be right. I read it was the US bound amps that shipped with 6550s. Someone said Marshall had a lot of problems shipping amps with EL34s because the EL34s would crap out before the warranty period was up due to the long ride here. 6550s are a more robust tube design, so they tweaked the circuit a bit for the swap.
They're saying modding a 2204 to use EL34s is really just rolling the amp back to how the English versions were made, if done correctly.
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Post by Leftee on May 12, 2021 6:32:33 GMT -5
Yep!
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Post by De ville on May 13, 2021 0:54:38 GMT -5
Okay, I bought it. Pictures will be forth coming. Amp sounds OMG!
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Post by Leftee on May 13, 2021 3:27:20 GMT -5
😎😎👍
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Post by Leftee on May 13, 2021 9:40:50 GMT -5
Congrats!
I had a ‘76 2204 back in the ‘80s. I wish I still had it.
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Post by De ville on May 13, 2021 20:44:26 GMT -5
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Post by Pinetree on May 15, 2021 11:02:43 GMT -5
Vertically stacked inputs... pfft.
Send it back.
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Post by De ville on May 15, 2021 11:14:17 GMT -5
They wouldn't take it back. Now I'm stuck with it.
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Post by Leftee on May 15, 2021 15:06:23 GMT -5
It’s the horizontal inputs in the ‘80s that get the bad rap - for whatever Internet reasons.
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