Metropoulos Forum

Look at the board from above with the tubes away from you and the pots towards you.

Not sure I should be telling you how to mod this if you are unsure what plate resistors are

Anyway, look at the board, first on your left are the cathode cap and resistor for V1 (shared on a JTM45)

Next turret is the V1a coupling cap and the V shape of two 100k resistors, these are V1 plate resistors the first goes to V1a (the first triode of V1) which is pin 1 of V1. The other 100k is plate resistor of V1b (to pin 6 of the socket).

If you add another plate resistor in series with one of these you will lower the plate voltage which will decrease the output of the stage, lower the headroom but also increase the gain (all things being equal given the Ck/Rk etc).

To achieve this you will need another turret near the one that hooks up to the coupling cap, then move the resistor to this and mount another 100k resistor to another turret. Mount the resistors in series with one end to the cap, a central tie point and the other to the blue plate wire to the tube. So now you have a 200k plate resistor in two parts. You need to decide if you are going to do this for V1a or V1b (only the channel you select will be affected. Now to make it switchable you will need a simple toggle wired with one wire to the mid tie point and the other to the other end of one of the resistors (I don't think it matters which) so that when you throw the switch it shorts out one of the resistors (ONLY ONE) such that you effectively bypass one of the resistors to make 100k again.

Open the switch and you go back to 200k. It does give more gain. On one of my hotrods I used 120k plate resistors on the extra gain stage board, only you can decide if you like it.

Of course all your wiring and grounds need to be perfect and the switch capable of handling 300v of dc

Thank you for clearning that up I thought it was there just needed to be sure I do some times check and re check but I only do that to be sure and also safe to me it is alright to ask to know you sure some one may have a better idea and or know better so really thanks again this b uilding this amp has been so much fun to me.

Well it is still running great and I could have done the layout neater than I did I am really trying to do this more neater it isstill the most hiss free amp I have and I have a marshall tube amp amd a HiWatt tube amp both 50 waters,right now Iam starting to do a big repair on my Peavey butcher the one made in the 80s.But just wanted to all who worked so much with me thank the jtm 45 plus is still going great Thanks again.

Excellent!!

What would be a good way to hook together my amp I built the JTM 45 clone four in put and my Marshall vintage modern ,how do I correctly do it to get the least amount of hum or hiss the marshall seems to be hum a lot at med to high volumns but when I link the two amps together with my chorus pedal o boy did I have a ground loop and hiss like I had a cb radio hooked up wrong .

I use a Lehle ABY with ground lift, individual adjustments.
If you are in US a radial equivalent is what I would use.

Thanks yes Iam in the states so I will look in to a ground lift type a b ab box so I can keep up with my drummer .

how is the one way I heard of linking two or more amps together on four hole malshalls like my jtm clone could I safty plug into the high input on the bright channel and then out of the low input on the bright channel in to the only one in put on my Marshall vintage modern ? Or is this not a good way or not safe.

Well I’m getting back in to it I have been taking w online tube amp course learning about all this stuff . And I’m going to be build a valve storm 100 Marshall with a master vol I just placed the other tonight making it the metro amp way this is going to be fun I’m wanting to add another gain stage doing three gain stages and the master volume and still build attenuators for it . I love that cranked Marshall sound

Good luck with the new build!

I got the 100 master volume parts I didn’t get a master volume pot what should I get on my tube depot kit I used a volume pot like the others not a double pot? I also didn’t get the transformers where do you guys suggest mojo tone?

A standard CTS or Alpha pot will be fine for the MV. This circuit does not use a PPIMV style master volume so you don't need the expensive double pot. Just get the same type of pot that you purchased for the rest of the build and you will be fine. As for the transformer, you can order the Metroamp spec trannies at the Metroamp webstore. Marstran also sells very nice iron that is custom wound by Heyboer. Mojotone also offers Heyboer but they may not be exactly the same spec as the Metroamp or Marstran.

As Dan said CTS or Alpha 1Meg Audio (AKA LOG) pot will do just fine (if you got a 4 holer set of pots by mistake they are the same as the MV two hole amps).

Well I ordered the parts for a 100 Marshall with a master volume from valve storm and figured I would get transformers from triode electronics I have he’d good luck with classic tone transformers in my other build a jtm 45 clone classic tone is out of business and there are no other transformers out there I can find so far I have tried three places all day back ordered any ideas?

Be very careful with Triode. I have had good dealings with them years ago but lately, there have been quite a few threads about folks purchasing items and waiting weeks with little to no communication from them. Trying to reach them on the phone is near impossible. I'm not saying that you won't receive your items but don't be surprised if it takes an unusually long time.