Park 75

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Hello DIYer's, I enjoy building amps as a hobby, but i'm daunted by the maths involved in straying from the tried and tested so have only made amps with well detailed schematics. I would like to do a Park 75 but no schematic is available. So far i have gathered snippets of info and i'm trying to glue them together. I have the PT but now need to find the right OT. Tranny will put out 530v . The 2 KT88's ( from snippets ) require 6000 to 12000 ohm anode to anode ? Does anyone know how to work out the true value? Or better still have a schematic. Cheers Longscale
 
Thanks jazbo8, Thats one number confirmed, have you ever seen a schematic ? In other forums i have read they say "just a Plexi with a hot preamp and beefed up OT for the KT88's". I wonder if by that they mean a cascaded input stage and maybe used the 100w OT. I'll keep searching. Cheers
 
No, never came across a Park schematic... I think the Plexi preamp should have enough grunt to drive the KT88's, so little or no modification would be necessary. In any case, you can breadboard it and see what happens. Good luck with your project!
 
You will find 100W Park schematics using 4 x EL34/KT77 .
Lacking the original 75W one I would build the 100W one in full, except using 2 x KT88 or whatever you like and proper supply/biasing/OT fo them.

You would very probably get 75W out of a pair and have full Park flavour.
 
WHat KP said is optimum but after some searching, j8 is correct. Marshall used their std. 50 watt OTs for the Park 75. Other sites have said that the PT used is from a 100 watt Plexi, but with 530 volts, they probably made some up especially for this amp.
The original Marshall 200 (PIG) that Ronson used had the 2.25K primary OT using 4 - KT88s, which is right in line with 4.5K for a pair of KT88s.

Here's a post that may help you:

Vintage Amps Bulletin Board • View topic - Park 75 vs Marshall 50

Here's another post that says both transformers on the Park 75 are the same as a Marshall 50 watter but 420vdc isn't enough voltage to make 75 watts from 2 KT88s:

Park 75. | MarshallForum.com
 
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That's what I gathered as well - "you can have whatever color you want as long as it's black" - for the Marshall/Park amps, you always get 50W - 3.4k, and 100W - 1.7k. At least, it kept the parts inventory down. 🙂
 
Thanks for the feedback, i am still finding bits of information , all conflicting. You would think there would be a schematic somewhere but have found others have been searching since 2004 with no luck

Strictly friendly curiosity 🙂 .... why do you want to build just *that* amplifier? 😕

Absolute worst case, why not straight the 100W (or 50W) versions which seem to be available?

Or if you want KT88 in the mix, all evidence and anecdote points to it being a "boosted 50W one", as mentioned above "a 50W amp, including standard Marshall 50W OT, with KT88 and a custom wound higher voltage PT" .... which is achievable 🙂
 
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