NewReligion
Well-Known Member
EDIT:
Perhaps this is not as rare as I initially believed it to be.
I’m finding a second of my 50 watt (2204) from 1976 PT is also a 1202-164. It measures 364VDC with AC Heaters at 6.124VAC.
A simple compilation at first. But I plan to build a data library of Dagnall/Drake PT & OT with actual voltages &!wire color to match the models & years however possible.
Perhaps the following has been discussed but I had a pleasant surprise.
Original Post.
(Discussed at End-Transformer Content).
I bought a ”Rescue” Marshall as I refer to the vintage amps that have been drilled on etc…
This is my 3rd from 1976. I have a line on a set of OEM black bat toggles but I’m not in any hurry there as I installed a matching set of metal toggles.
The amp was/is a Marshall Model 1987. The iron is all stock (This is the main subject). The faceplate was wasted in addition to someone drilled a 3/4” hole to install a 12VAC Fender style Indicator Light. All the pots remarkably are intact & functional.
I rewired the 120VAC/Switches/Mains Fuse/PT network. Replaced the faceplate & installed a 120VAC Marshall Indicator Light.
I completed my new “Divergent” circuit. The circuit signal sounded & felt weak. That is to say not making the cut.
I always fine tune every amp I work on but this was where it became interesting to me. I went ahead & installed a buffered loop. Then, in order to start tuning the amp I checked the bias which I normally do first thing.
When checking the VDC on the Mains Fuse & JJ E34L pin 3 I got 400VDC under load at idle, all volumes at zero. I thought this didn’t seem correct for a 1976 50 watt. I checked the numbers on the PT & OT.
I was pleasantly surprised to discover the Drake set to be a PT 1202-164 & the OT a 784-139. These Transformers were used in “US” amps from 1969-1973. The UK PT in 1969 was a lay down.
I can understand how Jose Arredondo liked the higher voltage of 500VDC for his clipping circuits but this is a different animal. No clipping diodes or transistors, no cathode follower, four stages of gain, nice & brown.
If anyone has additional information to add, challenge or correct, I am open to it as I am about to start assembling a list of Marshall Transformer data.
I did go back in & add dampener/swamp resistors. The Screen resistors on the power tubes are 5 watt 1k.
I did not add any type of Resonance mod. The NFB is 100k on 8 ohm tap.
Feel free to take this any where you like.
I would really like to hear or should I say read more data on the Drake & Dagnall Iron sent to the US from 1969 to 1981.
Thanks, David
Perhaps this is not as rare as I initially believed it to be.
I’m finding a second of my 50 watt (2204) from 1976 PT is also a 1202-164. It measures 364VDC with AC Heaters at 6.124VAC.
A simple compilation at first. But I plan to build a data library of Dagnall/Drake PT & OT with actual voltages &!wire color to match the models & years however possible.
Perhaps the following has been discussed but I had a pleasant surprise.
Original Post.
(Discussed at End-Transformer Content).
I bought a ”Rescue” Marshall as I refer to the vintage amps that have been drilled on etc…
This is my 3rd from 1976. I have a line on a set of OEM black bat toggles but I’m not in any hurry there as I installed a matching set of metal toggles.
The amp was/is a Marshall Model 1987. The iron is all stock (This is the main subject). The faceplate was wasted in addition to someone drilled a 3/4” hole to install a 12VAC Fender style Indicator Light. All the pots remarkably are intact & functional.
I rewired the 120VAC/Switches/Mains Fuse/PT network. Replaced the faceplate & installed a 120VAC Marshall Indicator Light.
I completed my new “Divergent” circuit. The circuit signal sounded & felt weak. That is to say not making the cut.
I always fine tune every amp I work on but this was where it became interesting to me. I went ahead & installed a buffered loop. Then, in order to start tuning the amp I checked the bias which I normally do first thing.
When checking the VDC on the Mains Fuse & JJ E34L pin 3 I got 400VDC under load at idle, all volumes at zero. I thought this didn’t seem correct for a 1976 50 watt. I checked the numbers on the PT & OT.
I was pleasantly surprised to discover the Drake set to be a PT 1202-164 & the OT a 784-139. These Transformers were used in “US” amps from 1969-1973. The UK PT in 1969 was a lay down.
I can understand how Jose Arredondo liked the higher voltage of 500VDC for his clipping circuits but this is a different animal. No clipping diodes or transistors, no cathode follower, four stages of gain, nice & brown.
If anyone has additional information to add, challenge or correct, I am open to it as I am about to start assembling a list of Marshall Transformer data.
I did go back in & add dampener/swamp resistors. The Screen resistors on the power tubes are 5 watt 1k.
I did not add any type of Resonance mod. The NFB is 100k on 8 ohm tap.
Feel free to take this any where you like.
I would really like to hear or should I say read more data on the Drake & Dagnall Iron sent to the US from 1969 to 1981.
Thanks, David
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