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Pitiful X-202

dcgillespie said:
That's the nice thing about Sams. Since I've already given you the Sams part number, you can just look at their under chassis pic, look for those part numbers, and then know exactly where those components are.

Good luck with it!

Dave
Click to expand...

Ummm, yeah (squint)...sort of...(more light, clean glasses)...
I've even gotten enlargements done at Kinko's...
I think I just soldered a green jewel where C41 is supposed to go.
 
I'm with you on that one for sure! But if the Sams folders are bad, then the downloaded and printed Fisher schematics are near impossible to use.......

Dave
 
dcgillespie said:
Those are the heater wires and are on pins 4&5 (not 2&3). Solid wire is nice to use, as it can be formed into position, and it will hold that position. Stranded wire will not hold a formed position nearly as well without significant work. If the tubes have run hot, then cracking is not uncommon. There's little danger if you don't replace them at this time, but if you do, 20 ga wire works well in this application.

Dave
Click to expand...
my local shop caries solid-core "hookup wire" in 22 ga... would that still be OK to use?... or would I be better off to use 18 ga (which I might be able to get)

thanks
 
You'd be better off in using 18 ga. You want the heaters to have the full benefit of the required voltage, without any of it being dropped unnecessarily in the wiring. The larger gauge wire will be a little harder to work with, but you should still be able to do a neat job of it -- particularly if it is solid strand.

Dave
 
thanks... actually, I've always wondered about stranded vs. solid wire... is there any benefit to using either, and if given the choice, which is better?... I've seen both used inside of my vintage solid state and tube equipment
 
Hi Dave. I just opened a thread on substituting audio trans, but no takers. I am particularly interested in your opinion. If you have the time or inclination please look at it. Thanks m artin
 
is there a way to set the "Phase Inverter Adjustment" on this X-202 amp using only a digital multimeter?

if not, is setting the pots at the middle position good enough?

also wondering how much difference getting this set perfectly makes with the amp.. is it mainly a sound quality thing?

thanks
 
I don't know about setting it with just a DMM, as I'm not that familiar with the circuits. Dave G. would probably know for sure. But settting in the middle is close enough to balance the sides enough. It's somewhat of a sound quality thing as it balances the sides of the push-pull as far as the phase inversion is concerned, as it minimizes distortion between the upper and lower 1/2's of the push-pull. P.I. should be as close to 180* as possible,IIRC to minimize distortion. That's how understand it.
 
There were different versions of this unit regarding specifically the phase inverter circuits. To know how to answer your question, I will need to know what value resistor is connected to pin #1 of the phase inverter tube: 18K? or 68K?

Dave
 
OK -- You have an earlier version like mine. As a result, you can follow the exact procedure I developed that Larry published as a sticky then (remember, it is done with the power OFF):

1. Use a jumper clip lead to ground the power supply side of R106 and R107.

2. At each driver tube, measure and record the resistance from pin #1 of each driver tube to ground.

3. Adjust the Phase Inverter control of each tube so that the resistance from pin 3 to ground matches the respective resistance measured from pin 1 to ground.

4. Remove the jumper clip lead, and that's it.

I hope this helps!

Dave
 
Pahse Inverter
dcgillespie said:
OK -- You have an earlier version like mine. As a result, you can follow the exact procedure I developed that Larry published as a sticky then (remember, it is done with the power OFF):

1. Use a jumper clip lead to ground the power supply side of R106 and R107.

2. At each driver tube, measure and record the resistance from pin #1 of each driver tube to ground.

3. Adjust the Phase Inverter control of each tube so that the resistance from pin 3 to ground matches the respective resistance measured from pin 1 to ground.

4. Remove the jumper clip lead, and that's it.

I hope this helps!

Dave
Click to expand...
excellent... I will be doing this for sure... thank you!

Q: does this Phase Inverter adjustment have anything to do with bias & dc balance settings?.. ie., should I do one before the other, and/or are they interdependent at all?
 
getting very excited, the work on my X-202 is almost finished, and I will be powering up soon

Q: when I do the bias setting, do I have to use 8 ohm / 100W dummy loads -- OR -- can I use my speakers instead?

(asking because my 8 ohm dummy loads have been ordered, but not arrived yet)

thanks
 
Setting the Phase Inverter adjustment in this manner, it is completely separate from that of the DC Bias/Balance controls. Therefore, they will not interact with each other.

Dave
 
before I set the dc balance and bias, where's the best place to have the adjustment pots so that I don't power up into a "red plating" situation... both preset in the approx. center of rotation range, or ???

thanks
 
DC Balance centered, and the bias pots to give maximum voltage (B- from the caps). This setting will drive the tubes at the coldest bias.
 
dcgillespie said:
Which on the 202, will be with the bias controls turned fully counter clockwise.

Dave
Click to expand...
thanks Dave!... I'm on track to try a power up later today (yikes, getting nervous and hoping for no smoke or fireworks...)

Q: what do you recommend for ideal bias setting for NOS Russian 6P14P-ER "Reflektor "tubes? (ER suffix 10,000-hour rated tubes)

thanks
 
I would go with the factory setting of 30 mA per tube. In my own unit, as well as other X-202 and SA-100 amplifiers I've worked with, the lowest distortion is produced at that setting (well, closer to 31 mA on average, but close enough). The Russian tubes should be able to handle it just fine. The optimum bias setting is only marginally a function of the particular tubes chosen (by brand, manufacturer, etc.), and virtually entirely a product of the circuit design they operate in. Of course, various tubes will all need their own particular setting to achieve that target, but the target itself always remains the same for a given circuit design and tube type, unless it is just an unreasonable operating point to begin with -- and there's a few of those units out there!

Dave
 
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