Tremolo 50

LoudStroud

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Recently picked up an early ‘68 plexi Tremolo 50 head. Based on the early official Marshall schematics, I had always thought it was a Lead 50 circuit (split cathode on V1, etc) with the added tremolo. But it turns out every Trem 50 I’ve seen internal pics of thus far, including mine, directly followed the JTM 50 circuit (JTM-45 w EL34’s and solid state rectifier). In fact, mine has the chassis that could be mounted in the 212 combo configuration. Also has earlier larger potentiometers found in Bluesbrealer combos and JTM-45’s

Haven’t studied the 100 watt Super Tremolo heads to see if they follow suit.

Moral of the story… if you have an opportunity to pick up a Trem 50, which are often available for a few less $$ than the non-Trem counterparts, don’t pass it up.
 

neikeel

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The Lead version for 50 and 100 came about in late 68/early 69 AFAIK @TAZIN will probably know when
I have a 68 which is early lead spec (ie virtually bass spec plus bright cap!) but tube rectifier (I rebuilt it but you could tell from the marks on the chassis it was originally tube rectified.
 
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TAZIN

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As far as I can recall all the '68 50w Tremolo amps (T/xxxxx) I've seen had the Bass circuit.
 

LoudStroud

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As far as I can recall all the '68 50w Tremolo amps (T/xxxxx) I've seen had the Bass circuit.
Essentially the same, but with a 250uF (instead of 320) cathode bypass cap and an added 100pf dog bone bright cap.
 

TAZIN

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Essentially the same, but with a 250uF (instead of 320) cathode bypass cap and an added 100pf dog bone bright cap.
They used both; 250uF and 320uF, cathode bypass caps in '68. The style of the 100pF volume pot bypass cap varied.
 

LoudStroud

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Here are pics. Took these at time of purchase. Some electrolytics had already been replaced. Since then, I've replaced the two main power supply cap cans. Originals were 40 / 40 uF. Appears the dual power supply cap can on tag board was replaced with original values, although might've been 16/ 16uF. Cathode bypass cap on V1 appears replaced as well
 

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LoudStroud

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What was also interesting about this Trem 50 is that it came from the factory w 82k bias feed resistors vs the expected 220k, as seen in this photo.
 

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TAZIN

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Actually they look like 68K resistors; nonetheless, it is an interesting factory mistake. I'll have to check some of my Tremolo files for other examples.
 

LoudStroud

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Actually they look like 68K resistors; nonetheless, it is an interesting factory mistake. I'll have to check some of my Tremolo files for other examples.
oops, yes. 68k. not sure why I had 82k in the brain. Yes, it is curious why it came with 68k's. Mistake seems possible. Amazing they lasted in there that long without being swapped out. Let me know if you come across any other similar. I've yet to find any photos from that period with anything other than typical 220k's.
 

TAZIN

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oops, yes. 68k. not sure why I had 82k in the brain. Yes, it is curious why it came with 68k's. Mistake seems possible. Amazing they lasted in there that long without being swapped out. Let me know if you come across any other similar. I've yet to find any photos from that period with anything other than typical 220k's.
I checked my Tremolo files and all of the examples had 220K resistors.
 

LoudStroud

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I had wonder the same thing. Or KT66’s maybe? But even my Park 75 w KT88’s has 220k’s
 

neikeel

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KT66 run fine with 220k
KT88 have smaller grid leaks ie 68k/82k region
 

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