1968 plexi PT now back down

FogDweller

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Last year I told forum members about a 1968 plexi (1959) I purchased for $2,099 from an online music store. While the shop said they had a tech go over it and it was working fine, I took a chance. The head shell had quite a bit of wear (fan installed then removed, spray paint, etc.) and a pre-phase inverter MV had been installed, but it sounded fantastic. Truly a wonderful sounding amp.

However, the old replacement Dagnall PT was a stand up, having been replaced decades ago. A friend, Scott Dickson, who’s also a great amp tech, encouraged me to get the transformer back down, as a few of you forum members did at the time. It was good advice.

Well, it’s now complete. Scott got the PT back down on the chassis this week. (The website that had the bracket was out of them for many months so it took a while). Now the amp is closer to stock. I’m very happy. I like the MV so that’s staying in for now. Scott also installed new F&T filter caps.

Before and after pics below. That’s it for the update.
 

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neikeel

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Looks much neater.
Did you find the cap change made any difference (presume 100-100 and 32-32) ?
 

FogDweller

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Looks much neater.
Did you find the cap change made any difference (presume 100-100 and 32-32) ?
I don’t have it back yet, and I’ll have to defer to Scott. I’ll have him weigh in.
 

Dr.Twang!

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Looks much neater.
Did you find the cap change made any difference (presume 100-100 and 32-32) ?
Good morning, all.
This is an interesting amp!
10K serial # with 12k specs, transitional mains/screen supply filters on the board, but PI and preamp capacitors on top of chassis….phase inverter cap down next to power transformer, preamp at other end.
PT is Dagnall T2562 that was double-belled and standing up.
@FogDweller asked if we couldn’t lay it back down as it obviously was at one time years ago. A bracket was sourced. Horrible old lead dress was redone and cleaned up and the PT is once again laying down as it should. Used one original bell with brackets removed for top cap.
Amp came in at 100/100 and 50/50 and sounded so good, we decided to leave those values as it would be easy enough to change the preamp reservoirs to taste later. The mains/screens filters were Illinois though, (is there an Illinois in China, too?) and looked a little sketchy and so have been changed out with Fischer & Tausche.
It’s hard to tell if it sounds better because it sounded so good to start with.
Also interesting is it appears the 47k NFB resistor connection to speaker common is original rather than 47 or 100k/8 ohm tap as in later iterations.
The amp has an easily removable Ken Fischer type 4 pre-phase inverter MV that sounds great- so good, in fact, that I have installed one on my bone stock 72 Superlead (photo in my avatar) in one of the 4 speaker jacks as it doesn’t seem to impede or change the NFB circuit like the LarMar or Frondelli MV seem to do. George M has written a bit about why he has chosen the pre-phase inverter MV and I do hear/feel the difference at stage volume.
At this point I feel that @FogDweller has saved another small piece of history by helping to preserve and rehabilitate this one from the excess and debauchery that was the 80’s.
 
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Dogs of Doom

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Good morning, all
This is an interesting amp!
10K serial # with 12k specs, mains/screen supply filters on the board, but PI and preamp capacitors on top of chassis….phase inverter cap down next to power transformer, preamp at other end.
PT is Dagnall T2562 that was double-belled and standing up.
@FogDweller asked if we couldn’t lay it back down as it obviously was at one time years ago. A bracket was sourced. Horrible old lead dress was redone and cleaned up and the PT is once again laying down as it should. Used one original bell with brackets removed for top cap.
Amp came in at 100/100 and 50/50 and sounded so good, we decided to leave those values as it would be easy enough to change the preamp reservoirs to taste later. The mains/screens filters were Illinois though, (is there an Illinois in China, too?) and looked a little sketchy and so have been changed out with Fischer & Tausche.
It’s hard to tell if it sounds better because it sounded so good to start with.
Also interesting is it appears the 47k NFB resistor connection to speaker common is original rather than 47 or 100k/8 ohm tap as in later iterations.
The amp has a Ken Fischer type 4 pre-phase inverter MV that sounds great on this one- so good, in fact, that I have installed one on my bone stock 72 Superlead (photo in my avatar) in one of the 4 speaker jacks and doesn’t seem to impede or change the NFB circuit like the LarMar or Frondelli MV seem to do. George M has written a bit about why he has chosen the pre-phase inverter MV and I do hear/feel the difference at stage volume.
At this point I feel that another small piece of history has been somewhat preserved and rehabilitated from the days of excess and debauchery that were the 80’s.
:welcome:to the forum Twang...

:cheers:
 

nasticanasta

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Last year I told forum members about a 1968 plexi (1959) I purchased for $2,099 from an online music store. While the shop said they had a tech go over it and it was working fine, I took a chance. The head shell had quite a bit of wear (fan installed then removed, spray paint, etc.) and a pre-phase inverter MV had been installed, but it sounded fantastic. Truly a wonderful sounding amp.

However, the old replacement Dagnall PT was a stand up, having been replaced decades ago. A friend, Scott Dickson, who’s also a great amp tech, encouraged me to get the transformer back down, as a few of you forum members did at the time. It was good advice.

Well, it’s now complete. Scott got the PT back down on the chassis this week. (The website that had the bracket was out of them for many months so it took a while). Now the amp is closer to stock. I’m very happy. I like the MV so that’s staying in for now. Scott also installed new F&T filter caps.

Before and after pics below. That’s it for the update.
Thus is so typical of people chasing tones
 

Spooky88

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I’d like to hear this amplifier please. If possible with both an active pickup setup and passive pickup guitars. I know I’m demanding. Haha! Great post!
 

neikeel

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Good morning, all.
This is an interesting amp!
10K serial # with 12k specs, transitional mains/screen supply filters on the board, but PI and preamp capacitors on top of chassis….phase inverter cap down next to power transformer, preamp at other end.
PT is Dagnall T2562 that was double-belled and standing up.
@FogDweller asked if we couldn’t lay it back down as it obviously was at one time years ago. A bracket was sourced. Horrible old lead dress was redone and cleaned up and the PT is once again laying down as it should. Used one original bell with brackets removed for top cap.
Amp came in at 100/100 and 50/50 and sounded so good, we decided to leave those values as it would be easy enough to change the preamp reservoirs to taste later. The mains/screens filters were Illinois though, (is there an Illinois in China, too?) and looked a little sketchy and so have been changed out with Fischer & Tausche.
It’s hard to tell if it sounds better because it sounded so good to start with.
Also interesting is it appears the 47k NFB resistor connection to speaker common is original rather than 47 or 100k/8 ohm tap as in later iterations.
The amp has an easily removable Ken Fischer type 4 pre-phase inverter MV that sounds great- so good, in fact, that I have installed one on my bone stock 72 Superlead (photo in my avatar) in one of the 4 speaker jacks as it doesn’t seem to impede or change the NFB circuit like the LarMar or Frondelli MV seem to do. George M has written a bit about why he has chosen the pre-phase inverter MV and I do hear/feel the difference at stage volume.
At this point I feel that @FogDweller has saved another small piece of history by helping to preserve and rehabilitate this one from the excess and debauchery that were the 80’s.
The serial is not that odd for a late 68 plexi.
The serial is not straight 10xxx it is SL/A10xxx which does include the first amps with preamp can and pi can up top on the chassis. These followed the 12series. The true 10series were late 67/early 68 and can be seen as shared v1 cathode with Drake -132OT and split cathode with Dagnall C1998OT. Typically double drilled for the OTs (I’ve had two).
Glad it got a sympathetic tidy up and tune up.
 
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Derrick111

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Looks like a nice tidy-up job and much better back to original. I love when people honor the original amp rather than trying to make it something it never was, and you have done just that. I'd say $2200 for this amp was a steal! Can't wait to hear clips...
 

matttornado

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Congrats! that is one fine amp you have there! Question about the pre-phase master:

Does it still allow maximum preamp gain? I tried that same pre phase master on my 1974 1959 superlead but it didn't allow the amp to reach max distortion.
 

FogDweller

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Looks like a nice tidy-up job and much better back to original. I love when people honor the original amp rather than trying to make it something it never was, and you have done just that. I'd say $2200 for this amp was a steal! Can't wait to hear clips...
Thanks, Derrick. I plan to record a demo on and upload it on here or YouTube. I’ll let the forum know.
 

FogDweller

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Congrats! that is one fine amp you have there! Question about the pre-phase master:

Does it still allow maximum preamp gain? I tried that same pre phase master on my 1974 1959 superlead but it didn't allow the amp to reach max distortion.
Thank you.

I believe so, yes. It certainly seems like max gain to me.
 


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