Hello from Toronto, Canada

[Princeoliver]

Hello!

Thank you for acceptance!

My uncle recently ask me to sell his PV2 and MV75 which he has owned new since around 1983. He haven't turn these on for about 10 years. I am thinking of buying these from him or my friend might if the cost of restoration is not too much. My friend is actually quite handy with recapping, etc.

Upon advice, I did mange to power them up last week. Initially, connecting the PV2 to MV75 there was distortion.

Then I when on to isolate where the problem lies. Connecting the PV2 to a Marantz power amp, it seems the pot needs good cleaning or there might be some other issues with preamp. The volume jumped up substantially as I turn the pot! But there was no distortion.

Connecting the MV75 to a Marantz pre amp, there was still distortion.

Since then I have given the PV2 to my friend. He told me today, he managed to clean the pot by taking the front faceplate off. But he has not turn it on to try as he feels it is too dangerous. He believes, the caps should definitely be changed.

I just bought over the MV75 to my friend today. He will take a look at it.

Might anyone know the cause of the volume jumping up and distortion? What other things should we look at to safely put the amps back in service?

Finally, how can we tell if I have a PV2 or PV2a or MV75 or MV75A, etc? I believe the amp is a MV75A or MV75AR as it has user replaceable fuse. Any help would be appreciated.

Thank you to all again in advance!

[roberto]

Hola, Change the volume control. You can get the same at parts connexion. It is not so difficult to do the change, but an electronic skills are needed. Usually the value of the control is 100K ohms. Only six cables are connected into the volume control. Just follow the same pattern of connexion. Take a pic of the cables of the volume control and place them to the new volume control exactly as it is. Change one at a time. This way you won't make a mess.

Regarding the distortion, it looks that a bias resistor on the particular is open. Listen carefully to find which channels is causing the distortion. Usually a bad power tube makes the bias resistor to burn. This resistor, the value usually is 20 ohms/7watts.

Happy listening!

[admin]

Princeoliver, first, welcome to CJO, it's gret to have you with us.

As roberto indicated, these are the first things I would look at as well. The volume control should be a relatively easy replacement. The amp may be a little more difficult to diagnose but trying to narrow down by which channel(s) the sound is distorted will go a long way. We also have both the PV2 and MV75 schematics in our database so I would definitely download that to help troubleshoot.

Here is the link for the schematics download location: https://www.conradjohnsonowners.com/vie ... 07ed906d74

Good luck and let us know how it turns out.

[roberto]

My bad manners...please welcome to Conrad Johnson Owners Princeoliver!

Happy listening!