Need gain and freq parts.

[TLS Guy]

Ok, y'all, the double pot is the freq 40-180 marked C50K, and the single pot is the gain marked A50K. They both have a sticker that says Volume MG. They are double ganged with 3 points on each gang. RBH Sound does not have replacement pots. Any help finding these for sale would be appreciated, as I have learned there are many variables to the thousands of pots for sale.
View attachment 60464

Potentiometers are really hard to find these days, as they are not used much any more.

The volume control will be log taper.

I suspect the phase control is linear, and ganged controls are really hard to find.

Your volume control.

Your phase control.

 

[Todd00000]

Potentiometers are really hard to find these days, as they are not used much any more.

The volume control will be log taper.

I suspect the phase control is linear, and ganged controls are really hard to find.

Your volume control.

Your phase control.

Thank you!

 

[Todd00000]

After I get this fixed, I'll start a thread about who's speakers sound the best. LOL

 

[highfigh]

Italians don't care. This was in 2017. :lol:

OK, mark it with 'Alta'?

 

[highfigh]

The taper will be log or linear. I suspect the volume is log and the phase linear. The value and taper will be stamped on the controls.

Volume pots are almost always Log because, as you know, it fits our hearing but as to your comment that pots aren't used much, that's just wrong. They're used anytime a designer wants to avoid going into the realm of VCAs and VCFs (or digital control) when their use keeps the price low, yet the finished product works as intended. That said, those can still use pots and if noisy pots have never been a problem for a device, I suspect they have VCAs and VCFs.

Ganged pots, like these?

https://www.mouser.com/c/passive-components/potentiometers-trimmers-rheostats/potentiometers/?number%20of%20gangs=3%20Gang

 

[Todd00000]

I talked with RBH Sound again, and they suggested I buy a replacement amp like this:

https://www.amazon.com/gp/product/B0002KRAP6/ref=ox_sc_act_title_1?smid=AM0JQO74J587C&psc=1

 

[TLS Guy]

I talked with RBH Sound again, and they suggested I buy a replacement amp like this:

https://www.amazon.com/gp/product/B0002KRAP6/ref=ox_sc_act_title_1?smid=AM0JQO74J587C&psc=1

That is a lot more expensive than a couple of pots. If it were me I'd fix the one I had. The question is, do you have the skills to do the repair?

 

[Todd00000]

That is a lot more expensive than a couple of pots. If it were me I'd fix the one I had. The question is, do you have the skills to do the repair?

A friend has the skills and tools, but I can't find exact replacements.

 

[TLS Guy]

A friend has the skills and tools, but I can't find exact replacements.

You don't need, and won't find, exact replacements. The vales ARE exact replacements. If your friend can not neatly install those components I picked out for you, then he is not an experienced restorer. I would have no difficulty repairing that unit, and nor should he if he is competent.

 

[Todd00000]

You don't need, and won't find, exact replacements. The vales ARE exact replacements. If your friend can not neatly install those components I picked out for you, then he is not an experienced restorer. I would have no difficulty repairing that unit, and nor should he if he is competent.

Again, thank you, I will order them today. My friend is an electrical engineer. If he changes his mind I'll contact you.

 

[Eppie]

Again, thank you, I will order them today. My friend is an electrical engineer. If he changes his mind I'll contact you.

We made need some more photos. It looks to me like the volume pot has 6 contacts and the phase pot twelve. If that's the case, the volume pot is a dual ganged pot and the phase pot is a double dual ganged pot. Volume pot should be available but if that's a 12 pin ganged pot for the phase, that will be harder to find. I would unsolder the pots from the board, pull them out and disassemble them to see if the tracks inside are broken or simply separated from the wiper. The metal tabs can be bent out to disassemble the pot and then bent and crimped back to close it up tight again.

 

[TLS Guy]

We made need some more photos. It looks to me like the volume pot has 6 contacts and the phase pot twelve. If that's the case, the volume pot is a dual ganged pot and the phase pot is a double dual ganged pot. Volume pot should be available but if that's a 12 pin ganged pot for the phase, that will be harder to find. I would unsolder the pots from the board, pull them out and disassemble them to see if the tracks inside are broken or simply separated from the wiper. The metal tabs can be bent out to disassemble the pot and then bent and crimped back to close it up tight again.

That is not a stereo unit, so the volume pot will have three contacts. It won't have more. The phase pot is a ganged double pot control and will have six contacts.
So I find it highly unlikely I did not spec. the correct replacements.

 

[Todd00000]

That is not a stereo unit, so the volume pot will have three contacts. It won't have more. The phase pot is a ganged double pot control and will have six contacts.
So I find it highly unlikely I did not spec. the correct replacements.

He's right and I was going to ask you that. The single pot has two gangs so 6 connections and the double pot has 4 gangs so 12 connections.

 

[lovinthehd]

While not as much of a project, you could perhaps entertain the idea of substituting a new amp/dsp.

 

[TLS Guy]

While not as much of a project, you could perhaps entertain the idea of substituting a new amp/dsp.

He's right and I was going to ask you that. The single pot has two gangs so 6 connections and the double pot has 4 gangs so 12 connections.

In that case you will not find a replacement, and you will have to ditch that amp, and send it to the recycling center.

 

[Eppie]

He's right and I was going to ask you that. The single pot has two gangs so 6 connections and the double pot has 4 gangs so 12 connections.

That's going to take more analysis then. Someone needs to look at the circuit board traces and see if all pins from the pots are being used. The volume pot may be only using 3 pins and the other 3 are just dummies so that the pot is mounted more sturdily. If one set of pins on each pot only has a round solder pad underneath and no traces leading anywhere, then it can be subbed with a single pot that is not ganged. If there are traces running from all 12 pins on the phase pot then you likely won't find a replacement and will need to replace the whole plate amp.

 

[Todd00000]

Thanks, y'all. I will do the trace and if I can't replace the pots I will get something like this:

https://www.amazon.com/gp/product/B09YLMGPY2/ref=ox_sc_act_title_1?smid=A39H8TQKROQAHA&psc=1

 

[TLS Guy]

He's right and I was going to ask you that. The single pot has two gangs so 6 connections and the double pot has 4 gangs so 12 connections.

That can't be right. The volume pots is single and the phase dual ganged. The outside of the unit shows a normal arc of turn. If the pots had more then one cursor, more than one cursor in each track it would not have that radius of a turn. I have been doing this for a very long time, and I have NEVER seen a volume control with more than three connections per channel and I can't conceive of a volume circuit that would require it. I would bet those controls I sourced will work perfectly.

 

[Todd00000]

That can't be right. The volume pots is single and the phase dual ganged. The outside of the unit shows a normal arc of turn. If the pots had more then one cursor, more than one cursor in each track it would not have that radius of a turn. I have been doing this for a very long time, and I have NEVER seen a volume control with more than three connections per channel and I can't conceive of a volume circuit that would require it. I would bet those controls I sourced will work perfectly.

Here are better pics.

 

[TLS Guy]

Here are better pics.

Yes, but those contacts are connected together, so effectively one contact. You absolutely can not have six contacts from one variable resistor. You have the contacts on each end of the resistor track and one for the cursor, that makes three. There is no other way to design or built it. Contacts which are joined together like that counts as one contact and NOT two.