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800-C Restore II

notdigital

notdigital

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I'm working on another 800-c and I've come across a couple of snags. The most immediate issue has to do with C-210 in the Multiplex Section.

The schematic calls for a polarized electrolytic. The cap I have on hand is a film cap. Is it OK to replace the 1uf electrolytic with a 1uf film cap in this location??? :scratch2:

Thanks!!
 

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should be fine. You can normally replace an electrolytic with a non-polar film as long as space allows.
 
I noticed on the 800-C parts list they used a couple of other low uF electrolytics: C65 - 2uF/70v and C67 - .5uF/350v

You might want to replace (if you already haven't) C111 - 8uF/50v
 
bhamham said:
I noticed on the 800-C parts list they used a couple of other low uF electrolytics: C65 - 2uF/70v and C67 - .5uF/350v

You might want to replace (if you already haven't) C111 - 8uF/50v
Click to expand...

Yeah, those are all gone. The only reason the question re C-210 came up is that I realized the replacement was a film cap. Aparently, it's no longer an issue :thmbsp:

Thx B
 
Another Question.......

Built myself an IBAM for Xmas but I have a connection question:

I removed R-119 and C-92 from the chain. Do I add a wire from the common NEGATIVE of the Dual Can to the bias wire lug?

Kinda makes sense since the resistor was removed but please let me know.

THANKS!!!!
 

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notdigital said:
Built myself an IBAM for Xmas but I have a connection question:

I removed R-119 and C-92 from the chain. Do I add a wire from the common NEGATIVE of the Dual Can to the bias wire lug?

Kinda makes sense since the resistor was removed but please let me know.

THANKS!!!!
Click to expand...


Good man :thmbsp:

That seems right to me - don't have an 800 schematic to hand. On the 400 all that is circled gets chucked then wire straight off the negative side to the IBAM.


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Bring it up slowly on your variac moving your trimmers while checking bias to make sure it's working like it should.
 
Thanks Bruce, just wanted to make sure. I don't have a variac so I just took a chance and it works fine, I think :scratch2:

My numbers:

V-14

Pin 3 466
Pin 4 431
Pin 5 82.3
Pin 6 -25.7

V-13

Pin 3 464
Pin 4 431
Pin 5 .254
Pin 6 -25.7

V-11

Pin 3 466
Pin 4 430
Pin 5 140.3
Pin 6 -25.6

V-10

Pin 3 467
Pin 4 430
Pin 5 55.1
Pin 6 -25.7

I switched the tubes around and the readings on Pin 5 followed the tubes fairly consistently. So I guess my hope for a good set of vintage 7591's is dashed, huh?? :dammit:

Other than a new set of EH's or NOS 7591's, what are my choices? This unit is really a backup unit that I'm putting in the attic so I wasn't planning on purchasing a set of primo tubes. I imagine I could leave the quad that's in there now since they play, in a distorted kinda way.......Nawww: I'll replace them. :yes:

Suggestions welcome :thmbsp: :thmbsp
 
Do your pin 5 measurements again. DC Voltage (autorange). And specify whether V or MV, please. Make real sure your ground lead is tight.

Larry
 
Yea, something's fishy with pin 5... with your IBAM you should be able to dial those in to something like 300mV (30mA) each. With 466 on your plates I wouldn't push it - maybe 32mA max. Raising the bias will drop your plate voltage a bit.

Pretty high grid & plate voltage, I suspect Con Edison is full steam ahead and pushing your mains to the limit. Might want to put a thermistor or two on the PT primaries or run a bucking trannie.
 
Concur on the Pin 3 and 4 voltages which should be about 430 and 375. Plus your bias voltage is way too negative. Bring it up to -20V and recheck all voltages. It should bring down the pin 3 & 4 voltages. Then check the ma (pin 5) on all tubes. Post results. Then we go from there.

Have you recapped or replaced the can's? The overly high plate and grid voltages can be indicative of weak Main Filter caps and or no real loading on the outputs.

As for the IBAM. Go straight off the cap to the IBAM, removing the 1K & 2.2K resistors, and the 1Kuf cap.

Larry
 
Gentlemen:

The holidays have taken me away from full attention to my 800-C. :D I decided, however, that I got a little ahead of myself when I installed the IBAM since there remained other preliminary items that needed attention, i.e. the top cans. So, I've removed the IBAM and installed a single pot in its place; I'll be using the single pot for all measurements until I am comfortable the unit is running as it should. (Preliminarily, the measurements seem correct EXCEPT for one tube that is running extremely "hot.")

I'll be replacing the top cans over the next week or so and then take measurements which I'll post.

Thanks all and have a Happy New Year!
 
Well, managed to knock out a few details, i.e. recapped the top cans, mounted the IBAM, installed test points and all is right with the world :music: :music: :music:

The 7591A's are small bottle General Electrics and Phillips tubes.

V-14

Pin 3 456
pin 4 417
pin 5 30.4
pin 6 -18.7

V-13 455

3 455
4 416
5 30.3
6 -19.1

V-11

3 454
4 415
5 30.7
6 -23.8

V-10

3 454
4 415
5 30.1
6 -19.4

V-11 with the 10K single pot ran a litttle high (52.5) The IBAM is able to tame it considerably :thmbsp:

Next stop: Gettting the tuner pointer to travel to the ends of the dial :scratch2:
 

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Test Points

I situated these so that they also fit with the larger EH 7591's
 

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Those voltages look good - just a bit high on the plate & grids which I suspect is from high house current. I like the inventive way you did your IBAM and test points. Well done :thmbsp: :thmbsp:
 
Thx Bruce.

Now for the last thing really bugging me:

I tested the range of the FM radio and while I can get 88.3 (WBGO) here in NYC, the other end of the dial reaches 107.1. There is another strong station at 107.5 (WBLS) but the drum doesn't turn that far. I opened it up and it looks like the wipers have maxed out their range will not travel anymore.

Any thoughts?
 
I read the alignment procedures in the manual: all electrical adjustments.

The issue I have is that the tuning capacitor or condenser will not physically go beyond a certain point, i.e. to the station here at 107.1 FM. The other end of the dial is fine. It picks up 88.3 (?) which is WBGO just fine. Actually, it goes beyond that to pick up a foreign language station which I never knew existed. It seems that if the condenser could be adjusted to shift right, it'll lose the foreign lang station but pick up 107.5. I just can't see how that is done, if at all possible.

BTW: Thinking it was the culprit, I detached the dial cord and manually turned the drum to it's max. It didn't bring in the station I wanted due to the physical limitation of the condenser itself.
 
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