Help : 50 watt 68 spec plexi build

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Help : 50 watt 68 spec plexi build

Post by Pat92 » Sun Nov 06, 2022 6:38 am

Hello guys here is what i'm looking to build :

- a 50 watt plexi with 68 specs : clearly looking for a VH sounding amp.
- With PPMIV
- Zero Loss FX Loop
- Finally a dual voltage virtual Variac

I have built many small amps threw schematics and wiring diagrams however my knowledge in amplification is limited to reading and duplicating.

Could you help to find wiring diagrams for what i'm trying to build ? Many links to the schematics are unfortunately not working anymore :( ...

And if it is possible to use a dual voltage virtual variac inside a 50watt plexi ? i have seen multiple 100watt diagrams with it but no 50watt.

Thank you for your help !

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Re: Help : 50 watt 68 spec plexi build

Post by danman » Mon Nov 07, 2022 6:46 pm

Here is the Metroamp instructions for the old 50 watt kit that they use to sell. It is a 68 spec plexi. The layout and schematic are down near the bottom. ... CTIONS.pdf

Valvestorm sells all of the parts that are used with the Metroamp instructions. He took over the parts when George stopped selling Metroamp kits several years ago.

This is a site hosted by one of our members. He has many of the old layouts that were once here on the forum. I believe the 100 watt dual voltage layout is there also. You may be able to transfer that to a 50 watt but you would need to figure some things out. The PT and power supply are different between the 50 and 100 watt model so you would need to adjust a few resistor values to make it work. If you have plenty of experience it shouldn't be difficult. If this is your first build, the dual voltage option will make the build much more complicated. You could try reaching out to Robert at Valvestorm and see if he can offer some advice on that subject. ... 549g-K1iDA

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Re: Help : 50 watt 68 spec plexi build

Post by neikeel » Sat Nov 26, 2022 12:13 pm

Marstran does a dual voltage PT that you could use. George used to sell a nice chunky switch for the virtual variac.

As danman days the 100w has a separate bias feed, whereas the 50w takes the bias voltage feed from a limb of the HT AC. It will work but you will need to experiment with the bias dropping resistor so that you get a consistent bias to the output valves.

The rest should be pretty straightforwards with the 50w build instructions now listed by Valvestorm and the loop will have its own instructions

Good luck, they are really good amps when well built and dialled in.

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