Finally acquired a X-202, but it has an issue

RS Steve

Tube Junkie
Subscriber
This is the one model that has eluded me for some time, but patience payed off and I was able to acquire one.
Problem is, the right channel is very weak. I have tried the obvious things to rule out controls, dirty sockets, and connections with no results. I guess the next step is to start taking voltages, but this chassis is quite different than the usual units I have restored.

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Weak whole channel could be any of a number of things.

One thing I would check first off, are the output tube screen resistor voltage dividers in the power supply. If the voltage on the screens of the output tubes is low, it definitely won't work right. There's big ceramic resistors near the output transformers (two pairs of resistors, one pair in front of the OPTs and one pair between the OPTs and the output tubes- one of each pair is for the left channel's tubes, the other for the right)- if the screen voltage isn't right on the suspect channel, it's time to check and compare the values of those resistors, to what they're listed as in the schematic.

Also, if the cap section in the can cap for the screen on that channel (there's separate screen supply caps sections for each channel, in the can cap nearest the rectifier tube) is partially shorted, it could also wreak havoc there. That amp looks to have never been recapped, so that's not impossible.

Check the bias too. If it's way too high or way too low,it will obviously cause issues... and each channel has its own bias pots and decouping (electrolytic) caps.

Also, how do you have the output terminals wired to the speakers? I usually like to start with both channel's negative speaker wires together on the "G" terminal, and the positives on the respective 4, 8 or 16 ohm taps. This takes the phase switch and the odd "damping control" wiring out of the picture. Less variables to start out with...

Regards,
Gordon.
 
I wired the speakers both ways, first like the manual with jumpers, then the negs to G and the pos to the respective 8 ohm tap. I will have to study how to bias the outputs, looks a bit crazy compared to my KX-200.
 
You will quickly see why I convert them to individual cathode resistors per output tube...

But, to be fair- it is simple to check the global bias for a channel, once you unsolder the jumpers across the 10 ohm resistors.

Regards,
Gordon.
 
Steve -- Replace the two big .68 uF mylar caps in the middle of the chassis. These are famous for going out on the X-202. Besides my own unit, I've probably restored at least half a dozen of these, and I haven't come across one yet where they were good -- or didn't go bad within mere minutes of applying power to the unit. Even if they aren't the problem (but there's a good chance it is), they need to be replaced anyway. There is a far greater chance that the electrolytic cans are still good than there is that these caps are still good, so replacing them would be a good first start. Replace them with 1.0 uF caps, which will help flatten the LF response of the design. Of the three cans, the one under the black cover is the most likely one to be bad if one is, so look at it too. It's the one serving the heaters and bias. If the output from the heater/bias supply is low, it's usually the selenium rectifier before its the black can cap.

Good luck with it!

Dave
 
Looks like it has had some repair work already, I'll have to study it for a while and see what needs to be returned to stock. Looks like rectifier diodes added to the rectifier tube socket, not sure if they bypassed the selenium or what. Two of the preamp caps have a tar like substance on them, someone please explain what that could possibly be.

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I guess the diodes are their to allow the use of the modern cheap rectifier tubes, looks like they gooped silicone on them to make sure they do not contact the bottom cover.
 
Looks like it's been pretty thoroughly recapped except for the small bias supply electrolytic decoupling caps. The two yellow caps with the goop on them are in the right channel tone control stage -- but it more looks like to me that the goop was applied rather than it oozing out from being defective. Couldn't hurt to replace them though. Looks like you're headed for some classic troubleshooting work!

Dave
 
Looks like it's been pretty thoroughly recapped except for the small bias supply electrolytic decoupling caps. The two yellow caps with the goop on them are in the right channel tone control stage -- but it more looks like to me that the goop was applied rather than it oozing out from being defective. Couldn't hurt to replace them though. Looks like you're headed for some classic troubleshooting work!

Dave
Yeah, I'm sure my head will be spinning in no time.
 
I ordered a complete can cap kit from HH, and I'll replace the selenium rectifier also. All these big ceramic resistors will be checked and replaced as needed also.
 
Thats just sad. Were they using left over Saran wrap for the film or something?

.68uf was a big film cap value back in the day. Probably had to use thinner film than usual.

They're also only rated at 250v stock- which would indicate fairly thin film. When I replace those, I just go back with a 600v or 630v (or at least 400v) cap. No reason not to, as even the modern 600v ones are no larger in physical size than the original ones.
 
Looks like it has had some repair work already, I'll have to study it for a while and see what needs to be returned to stock. Looks like rectifier diodes added to the rectifier tube socket, not sure if they bypassed the selenium or what. Two of the preamp caps have a tar like substance on them, someone please explain what that could possibly be.

I still suspect that can cap nearest the rectifier tube socket. That goes bad on one of the two sections for the screens, and you lose most of the screen voltage on that channel...

Regards,
Gordon.
 
.68uf was a big film cap value back in the day. Probably had to use thinner film than usual.

They're also only rated at 250v stock- which would indicate fairly thin film. When I replace those, I just go back with a 600v or 630v (or at least 400v) cap. No reason not to, as even the modern 600v ones are no larger in physical size than the original ones.

Yeah, I have a stock pile of 630V and 400V, I'm installing all new ones just to be sure. The seller graciously refunded me 150.00 for my troubles since it isn't working correctly, most certainly made my day. I'll have it fixed soon. :thumbsup:
 
I'm looking to replace C-7 through C-10 capacitors on this X-202, they are 25uf / 6V originally. What is the highest voltage rating I can get away with on these? I have found 16V, but not any luck for 6V.
 
50v max. 25v and 35v are prob most popular unless you replace a shitload of caps then most guys will go with one voltage. And that's usually 50v in my experience on both the tube and Solid State sides.
 
To get that low of a working voltage, you'll have to go with Tantalum capacitors. But 16 volt and even 25 volt caps will be fine: They won't remain formed as long as they normally would with just a volt or two across them -- but they'll almost certainly outlast any new power supply caps you're installing........

Dave
 
To get that low of a working voltage, you'll have to go with Tantalum capacitors. But 16 volt and even 25 volt caps will be fine: They won't remain formed as long as they normally would with just a volt or two across them -- but they'll almost certainly outlast any new power supply caps you're installing........

Dave
I found some 22uf 6V tantalum caps, they will have to do. :thumbsup:
 
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