4 pin rhodes power amp gets hot on one side

[Steve Conner]

When you record a Rhodes, do you even use the power amp and speakers? I'd imagine it getting plugged into the desk through a bunch of effects.

I have an interest in these old transformer driven power amps. I've built similar circuits with modern silicon transistors, and they make great guitar amps. If I thought germanium transistors would sound better, I'd go to the effort of finding them, but I don't think it makes a huge difference, certainly not enough to justify the high price and reliability hassles.

[Jazz P Bass]

O/k.
Here is the replacement parts from Vintage Vibe.
Link: Vintage Fender Rhodes piano suitcase peterson rebuild kit
I have also attached the amplifier picture from VV's site, listing the items that change.
And a picture of the OP's amp.
Looks like a no brainer to me.
Buy the kit!
I would not even be concerned about " changing the tone".
Make the amplifier work & enjoy it.

[R.G.]

The Vintage Vibe kit has the explanation that silicon is more reliable and sounds the same.

What a surprise.

[Jazz P Bass]

Some interesting info.
Delco's datasheet for the DTG-110B transistor, as applied to a 100W amplifier.
R.G Keen's well written foray into Vox amps.
http://www.geofex.com/Article_Folder...placements.pdf
Thomas Vox Solid State Amps

[Skiroy]

O/k.
Here is the replacement parts from Vintage Vibe.
Link: Vintage Fender Rhodes piano suitcase peterson rebuild kit
I have also attached the amplifier picture from VV's site, listing the items that change.
And a picture of the OP's amp.
Looks like a no brainer to me.
Buy the kit!
I would not even be concerned about " changing the tone".
Make the amplifier work & enjoy it.

Thank you so much,but are these the values of the new components or is it just point to the components that need to be changed?

Do we know the list of the new needed components. I am going to change to silicon and rebias my self. Honestly my biggest concern was keeping the original components fore sound,But I then realized:"For What"? I am recording direct bypassing the power amps any ways. But I will rebuild them for if I ever want to use it for performance or ect or if I ever sell it.

[Jazz P Bass]

Thank you so much,but are these the values of the new components or is it just point to the components that need to be changed?

Do we know the list of the new needed components. I am going to change to silicon and rebias my self. .

The parts supplier is not going to "give" you the values!
Duh.
There is a transistor & resistor kit (in the drop down menu) that is $20.00.
Buy that.
The $75.00 kit includes all of the parts that will "fully" restore the output section.
As to the values that you will need, that will take some severe thought & experimenting.
(Of which, the parts supplier has already done)
Truthfully, from what I have seen of your posts, I do not think you are up to this.
At this, I can only kindly advise that you take the amp to a qualified tech.

[Steve Conner]

You know the story about the consulting engineer who fixed a car assembly line by bashing it with a hammer, and sent in a bill for $10,000. The factory were surprised and demanded to see an itemised invoice. So he sent another bill:

One hit with hammer: $0.10
Knowing what to hit: $9,999.90

And so it is in this case. The kit contains about $15 worth of parts. You're paying for the time spent choosing the right component values, matching the transistors, testing, and writing the instructions. And maybe even the right to send it back for a refund if it doesn't work.

We say install some MJ15025s and change the 2.7 ohm resistors out for 12 ohm ones. But that advice is free, and may be worth it

[Skiroy]

The parts supplier is not going to "give" you the values!
Duh.
There is a transistor & resistor kit (in the drop down menu) that is $20.00.
Buy that.
The $75.00 kit includes all of the parts that will "fully" restore the output section.
As to the values that you will need, that will take some severe thought & experimenting.
(Of which, the parts supplier has already done)
Truthfully, from what I have seen of your posts, I do not think you are up to this.
At this, I can only kindly advise that you take the amp to a qualified tech.

They are n ot $20.00. It says -$20.00. So the cost would be $120.00 with shipping for $15.00 worth of parts,for both amps. And while I agree with you that I am not an electronics guy I certainly can change components out and meassure voltages. It is worth paying for the know how but If someone here has done it already and knows the resistor values and components that need to be changed and its a matter of swapping a few components,why not save myself a $100.00. Wow run on sentence. Sorry

[Skiroy]

We say install some MJ15025s and change the 2.7 ohm resistors out for 12 ohm ones. But that advice is free, and may be worth it

Is this a educated guess or from experiernce with doing this conversion?

[Steve Conner]

Read over the whole thread again carefully, and make your own mind up as to the value of the advice. Someone else suggested 12 ohms, and I think he may have tested it.

Also it is consistent with theory, silicon transistors need about 0.6V of bias, and if we take 35*(12/(820+12)) we get 0.5, erring a bit on the cold side for safety.

[Skiroy]

Last question. When buying resistors from mouser. Can I get any old 12ohm resistors or are they rated for quality? What should I be concerned with here? I mean can I go to radio shack or does this matter?

[Skiroy]

Got the VV kits. One last thing. As far as the 3 prong on my PSU. If I just leave it as a 2 prong and I am only using the rhodes preamp and not the power amps what is the risk? I know the ground is to prevent me from getting shocked but would leaving it as a 2 prong increase risk of my electronics in the rhodes? I see alot of these rhodes PSUs with the 3rd prong broken off. I rather not spend the time and money if its unneccessary but of course I will if its needed.

What do you guys think?

[gbono]

Please use a proper grounded mains cable on the electronics - it will not change the sound of your piano and it might save someones life - NO JOKE