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First project in my new cave... X-100

analog addict

analog addict

Glory or Death!
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Got my grubbies on this little beauty the other day....

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Not perfect by any means and a little smutzig...

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But a little scrubbing with some gentle cleansers might really make this elegant ol lady a real looker...

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But like any 50 yr old, there are a few scars. It was offered to me by another local AK'er who met me at a handy location half way between our place, HJS' House of Speakers....(basement's looking good with the new shelves!)

The only tube that was missing was the rectifier...:scratch2: Had kind of this yellow residue around the 5AR4 socket too. I missed it when I looked up the skirts last night, but I did know that it had been repaired in the past.

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Here's the kicker....

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D'Oh!...:saywhat:

Guess it's not going to be just a check up and a recap/change a few resistors....:sigh:

I gotta print off the schematic anyway. I'll need to add a snubber cap too.
I've done some reading, and know the PT is a weak spot.

This don't look original to me either....

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I'm going to take a closer look at this over the weekend, but there's gotta be someone out there in Fisherland who can just look at this and say that this part of the wiring is OEM or not...:thmbsp:

Also, am I correct in assuming that if I run 11 VAV in the PT's primary, I should get say 30-35 VAC out to the rectifier socket pins 2 and 4 via those white wires from the PT??? I know that's a weak point on these. I should get at least a 0.5 and 0.6/1.2 VAC set of secondaries, right?

Anyone have a suggested face cleaning fluid/method?

How's the spacexpander socket work? Jumpers between amp and pre? BTW, what's a "spacexpander" anyway? Hmmm, I wonder how a Carver C-9 would make this thing sound plugged in there....:scratch2:

Lastly, what's the scoop on the big wire wrapped/grounded resistor between pins 6 and 8 on the 5AR4?


TIA...:thmbsp:
 
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Yikes! Maybe the previous owner fried the 5V tranny winding and added diodes instead. Look for the yellow leads coming out of the power tranny and check them. If I were you I would put the rectifier back and ditch the B+ voltage dropping toaster coming off pins 6 and 8....I would suggest rebuilding the entire power supply based on the original schematic (attached).

Try putting back to stock
 

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Yes, i second replacing the whole power supply.
Test the transformers. This has been monkeyed with and you might have to unfix it as part of the power supply update.
That'll keep the power transformer solid in the future, assuming of course that it's Ok now.
Does this use 6BQ5s or 7868s?
 
audiodon said:
Yes, i second replacing the whole power supply.
Test the transformers. This has been monkeyed with and you might have to unfix it as part of the power supply update.
That'll keep the power transformer solid in the future, assuming of course that it's Ok now.
Click to expand...


First order of business is unscrewing the PT and seeing what is hiding underneath. I will be a bit disappointed if the 5V tap is dead, since I paid close to fair market value for this piece. Of note, you can see the cut yellow wire remnant on pin 8 of the 5AR4 socket. I'm hoping I'll find the yellow wires rolled up underneath the PT, but that may be a bit optimistic...:sigh:

audiodon said:
Does this use 6BQ5s or 7868s?
Click to expand...


One of the above pictures shows a couple of the output sockets, labeled EL84/6BQ5/7189. I have some Fisher labeled Mullards that will wind up in this if I can get everything back up to snuff...:scratch2:




Sam Cogley said:
On the bonus side, you have a complete set of early-style knob brights.
Click to expand...

Yeah that was a nice perk. First order of business was discovering that when you glue them back onto the knobs, you have to index them to make sure the little indent indicators line up with the faceplate markings.

I have a set of new brights for my A-19 Allegro, but they don't have the indents....
 
Because it has been repaired doesn't mean the repair didn't take. You'll have to pop the transformer leads and test for non-opens or shorts.
This is the kind of unit that front panels show up for on ebay because of power tranny problems.
7189s are 6BQ5s on steroid. I saw the size of that output iron. This will be a monster!
 
audiodon said:
Because it has been repaired doesn't mean the repair didn't take. You'll have to pop the transformer leads and test for non-opens or shorts.
This is the kind of unit that front panels show up for on ebay because of power tranny problems.
7189s are 6BQ5s on steroid. I saw the size of that output iron. This will be a monster!
Click to expand...

Well, I'd rather figger out a way of replacing the PT if necessary. It's a pretty unit, and would prolly sound very sweet when 100%.

I'll have to look at the output tube sockets and see how the pins are wired. I have a small collection of GE 7189A's that might also shine in this.

I'm actually going to take the PT off the chassis and pull the wire side bell off and see what happened to the yellow leads. Is this a mistake?

If not, wish me luck....:thmbsp:
 
audiodon said:
Because it has been repaired doesn't mean the repair didn't take. You'll have to pop the transformer leads and test for non-opens or shorts.
This is the kind of unit that front panels show up for on ebay because of power tranny problems.
7189s are 6BQ5s on steroid. I saw the size of that output iron. This will be a monster!
Click to expand...

I've bought three of these. The first two had bad power transformers. Unfortunately, power transformer issues are somewhat common.

Good luck.
 
It's a good idea to investigate the power supply transformer before doing anything else. X-101-Bs are also transformer poppers.
 
If the 5V winding is really toast, I would consider just rebuilding the power supply with fresh diodes and change the two 250ohm dropping resistors to something slightly higher to account for the higher B+. It will still be a decent unit....with one less tube to buy.

If you do decide to replace the power tranny it would be a good reason to find something with a separate winding so you could implement a fixed bias scheme and use it to create a DC source for the 4 12AX7's for phono & tone controls....similar to what is used in the Fisher 400/500/800 receivers.
 
Ok...

So here's what I got....Looks like an OEM PT although it has an "A" suffix....

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So what's the deal with this wrapped red wire...:scratch2: The plot thickens...

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Interesting.....

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Looks like both the thin and the thick wire originate from the same place. What's that all about???

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Did some variac measurements. With 11.8-12VAC, both the thick and thin wire are generating voltage. Good!

However, when turned up to 58-59 VAC, I'm getting 2.8-3.0 VAC on both the thick and thin wires, leading me to believe that these are both 6V taps.


Is this the way it's supposed to be, or do I need to tear the PT down even further???

Somehow I can't believe that the 5V tap is just a 6V tap with a dropping resistor....:scratch2:
 
We're kind of getting out of my level of expertise here, but how much voltage would go onto the primaries normally, 120 VAC, correct? Did something stop you from taking it that high?
 
audiodon said:
We're kind of getting out of my level of expertise here, but how much voltage would go onto the primaries normally, 120 VAC, correct? Did something stop you from taking it that high?
Click to expand...

Sam's folder says 117, but I just wanted to be cautious as far as putting voltage to it....
 
If you look at the notes on the sam's folder it will say something to the effect that voltage variances of 10-15% are normal. The 117 was for testing and to set a baseline. So if your wall voltage is 120 expect a slight variance in all voltages you get. As long as the variances are equivalent to the difference in line voltage, don't worry about it.

Larry
 
larryderouin said:
If you look at the notes on the sam's folder it will say something to the effect that voltage variances of 10-15% are normal. The 117 was for testing and to set a baseline. So if your wall voltage is 120 expect a slight variance in all voltages you get. As long as the variances are equivalent to the difference in line voltage, don't worry about it.

Larry
Click to expand...

Well, I ran the variac up to 117V as measured by my DVM, and both the thick and thin bare wires are measuring 6.8-7 VAC. The B+ voltage was spot on at 358-360 VAC.

I'm torn between attempting to tear down the transformer windings or just bite the bullet and buy a separate Hammond 117v:5V/2 or 3A transformer and hide it under the chassis. I'd really like to get the 5AR4 back into the mix, especially since I have an extra GE and an extra Raytheon/Made in Japan tube lying around.

Would an extra outboard 5V PT greatly affect the value?

Does anyone ever see these PT's come up for sale, and if so, how much do they run?

Anyone have any thoughts?
 
Analog.......
Before you do that, go back and measure the voltage of the other heater winding powering the EL84's and 12DW7's. My guess is that the funky wiring covered by red soda straws is your 5V winding and the heater winding that you measured at 7 volts is the winding for the EL84's (fat copper) and 12DW7's (skinny copper). Maybe the previous owner was worried about the heater voltage being too high with modern line voltage and decided to use the 5V for the heaters of everything else....and didn't want to replace the 5AR4. I suspect that you don't need a PT......
 
I agree with Dadbar. You don't have enough information yet, and you possibly have a fine transformer that just needs shrink wrap or teflon lead coverings.
 
Dadbar said:
Analog.......
Before you do that, go back and measure the voltage of the other heater winding powering the EL84's and 12DW7's. My guess is that the funky wiring covered by red soda straws is your 5V winding and the heater winding that you measured at 7 volts is the winding for the EL84's (fat copper) and 12DW7's (skinny copper). Maybe the previous owner was worried about the heater voltage being too high with modern line voltage and decided to use the 5V for the heaters of everything else....and didn't want to replace the 5AR4. I suspect that you don't need a PT......
Click to expand...

The red covered wiring is the thick and thin leads soldered together. They both read the identical voltage and by this picture supply the filiments of the 6BQ5's....

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In this picture you can see the yellow wire running from the 220 ohm resistor in the previous picture to the 4 output sockets.

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In fact it look to me like both the red wrapped wires are connected to the yellow wire by 220 ohm resistors. There's also an orange wire running to all the output tubes. It appears to be coming from the inner of the two can caps, which is connected to the rigged diode bridge via the two paralleled 125 ohm power resistors.

B+ to the 6BQ5's maybe?


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I'm guessing the brown and green wires are also heater wires, and they seem to come off the PT feed before the 220 ohm resistors.....:headscrat


I'll need to recheck the schematic and see how this compares to what was intended.

I wish I had the amp in front of me, but that is how it goes....:thumbsdn:
 
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