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 Post subject: Re: Strange Philco problem --need help
PostPosted: Mar Fri 23, 2012 9:22 pm 
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noisebox wrote:
6K6
V6 pins
2 = 6.3 vac
3 = slight -voltage
4 = 200vdc
5= slight - voltage
6,7,8 no voltage
Ben, well for starters, unless you find a broken wire between V6 pin 3 and your audio output transformer, it looks like you are going to be shopping for a replacement audio output transformer (this is your "crumbly" audio). The lack of voltage on V6 pin 3 is because there is an open circuit somewhere between the primary center tap of the audio transformer and the tube.

For what it's worth, you are looking for an audio output transformer with about 8000 ohm center tapped primary and 3.2 ohm secondary. Of course it needs to fit whatever physical dimensions are available for the original. It's probably about a 5 watt transformer. Perhaps an add over in the Classified section with the Philco part number would be a good idea.

If you are looking for a new transformer it might be close to a Hammond 125B, but that would run you about $35 new.

Curtis Eickerman

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 Post subject: Re: Strange Philco problem --need help
PostPosted: Mar Fri 23, 2012 10:39 pm 
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Location: 97381, USA
Thank you Curtis,
When I get home I'll check connections. Fortunately, if it is the OT I think I have an extra from the same model that was trashed. A transformer is not something I throw away so the chances are good I have one.

Another problem I have is the combination power switch tone control. When I rotate it clockwise it behaves as a volume control--which it is not. I've pulled the leads and tested it and the reading is right and the resistance values transition smoothly. Any ideas what might be causing this?
Thanks,
Ben


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Mar Fri 23, 2012 10:53 pm 
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noisebox wrote:
Another problem I have is the combination power switch tone control. When I rotate it clockwise it behaves as a volume control--which it is not. I've pulled the leads and tested it and the reading is right and the resistance values transition smoothly. Any ideas what might be causing this?
Ben, unless you have already replaced it, I would check and probably replace C29. If it is leaky or shorted then R19 will be essentially killing your audio when the center (which is ground) is adjusted upward toward the C29 end of the pot.

Curtis Eickerman

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 Post subject: Re: Strange Philco problem --need help
PostPosted: Mar Sat 24, 2012 12:21 am 
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Thanks Curtis, I'll look at that when I get home tonight.
Ben


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Mar Sun 25, 2012 6:08 am 
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From what I see on the schematic the orange wire is the CT of the OT and the blue wire and the white (which in the case of this transformer is brown) wires are the ends. Brown and Blue connect to pin 3 of the 6K6s. The transformer on the schematic says 300 ohms, which is from the CT to one of the ends making the transformer secondaries 600 ohms end to end or 300 ohms each leg.

Checked on the DDM:
The primary is right on at .4 ohms
CT to blue is .592 kohms
CT to brown is 249 ohms.
Looks like a bad transformer--or is it?

My replacement transformer might also be bad because it has similar readings.


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Mar Sun 25, 2012 7:09 pm 
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noisebox wrote:
The primary is right on at .4 ohms
CT to blue is .592 kohms
CT to brown is 249 ohms.
Looks like a bad transformer--or is it?
Well it may be bad, but your readings do not agree with your 6K6 voltage measurements. According to your voltage measurements there was no plate voltage getting from the CT to one of the 6K6s which would mean a total break, infinite ohms or extremely high. Your resistance readings are not saying this.

So, is the one that reads .592 Kohms (which is just 592 ohms) also the lead going to the tube that had no plate voltage? If so, it is remotely possible that there is a bad connection in the transformer and when moving things to test the resistances something is touching (poorly) which was previously not touching at all.

The 249 ohms sounds reasonable and adequately agrees with the 300 ohm reading that the schematic shows. Is this lead going to the 6K6 tube that had plate voltage?

Curtis Eickerman

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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Sat 07, 2012 8:44 pm 
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I replaced the OT with a Hammond 125C as recommended and still no go. I get sound but weakly. When I get home from work this evening I'm going to remeasure voltages and see if they changed or if I'm back at square one.
Ben


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Sun 08, 2012 12:09 am 
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noisebox wrote:
I replaced the OT with a Hammond 125C as recommended and still no go. I get sound but weakly. When I get home from work this evening I'm going to remeasure voltages and see if they changed or if I'm back at square one.
Ben
As I recall you had 2 problems. "crumbly audio" which is what the output transformer was to address (lack of plate voltage from the transformer to V6 pin 3). This is not expected to cure the other problem (lack of audio and improper operation of the volume control).

First lets see if you now have voltage on pin 3 of both 6K6 tubes.

Did you ever check or replace C29 as recommended earlier?

Curtis Eickerman

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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Sun 08, 2012 7:18 pm 
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This is a layout for the 46-1226 that Philco has in their service manual. Unfortunately, the numbers of the caps and resistors do not corespond to those found in the schematic. Could you please let me know which cap is C-29? This way I can quickly find what I'm looking for.
Thanks so much for the help!
Ben


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Sun 08, 2012 8:59 pm 
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Noisebox,

The Philco pictorial you excerpted in your last post doesn't match the Rider document you linked in your first post. Is the Philco document online? Link?

I don't think the Rider C29 appears anywhere in the Philco drawing excerpt. Perhaps it is located above the chassis.

The Philco drawing is incomplete, they have omitted all the wiring. And, I don't think all of the parts shown are connected in a way that can match the Rider schematic.

The Rider C29 that Curtis is asking about has one end connected to one side of the tone control, and the other to the plate ( pin 2 ) of the 7C6. The Rider schematic shows this as 0.01uF.

I'll second Curtis on the need for taking a new set of voltage readings, too.

Ted


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Sun 08, 2012 9:37 pm 
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This layout is exactly as the chassis appears when I'm looking at it. It comes from the service manual for the 46-1226 rev 221. Now I'm wondering why the riders schematic is different and in what way. I also have a schematic from the same packet that has the sections for each stage.

I'll be able to measure voltages this evening after work.
Ben


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Sun 08, 2012 9:44 pm 
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C29-now I know where to look. The tone control wasn't marked on the Riders schematic.
Thanks,
Ben


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Mon 09, 2012 2:27 am 
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noisebox wrote:
C29-now I know where to look. The tone control wasn't marked on the Riders schematic.
A layout from one source and a schematic form another can be confusing.

C29 goes from 7C6 pin 2 to one end of the tone control.

Curtis Eickerman

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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Mon 09, 2012 4:43 am 
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Replaced C29, still the same

6J5 pins
2 and 7 heaters 2.8 vac
3 = 98vdc
5 = 18.3vdc
8 = 30vdc

6K6
V6 pins
2 = 5.6 vac
3 = 171vdc
4 = 178vdc
5= slight - voltage
6,7,8 no voltage

V7 pins
2 = 5.6vac
3 = 167vdc
4 = 177vdc
5 = slight -voltage
6,7,8 no voltage

7C6 pins
2 =2.8vac
3 =1v
4,5,6,7 nothing or slight voltage
8=2.8vac


I think I had my variac set lower than my last measurements. The tone control still makes the volume cut out.


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Mon 09, 2012 4:54 am 
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Hi

Pin #2 on the 7C6 needs to be positive, DC, 50 volts or more. R15 (Rider schematic) , 220K, may be open?

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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Mon 09, 2012 5:06 am 
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R15 shows 3.3M on the Riders. Sure it's that one? Some of these numbers look like blobs.


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Mon 09, 2012 5:10 am 
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noisebox wrote:
R15 shows 3.3M on the Riders. Sure it's that one? Some of these numbers look like blobs.
The R1blob Norm was referring to might be R18. It's the plate resistor for that tube.

Curtis Eickerman

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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Mon 09, 2012 5:20 am 
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Found it on the chassis. I have a replacement but I'll have to wait until morning. Two days off to get this solved. Thanks for your patience.
Ben


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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Mon 09, 2012 3:43 pm 
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Hi

Curtis is right, it's R18. The one marked 220000. If open plate voltage will be missing on the 7C6 and who knows what the tone control will do? It's tied into this point through a cap.

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 Post subject: Re: Strange Philco problem --need help
PostPosted: Apr Mon 09, 2012 4:40 pm 
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R 18 was open. I replaced it and now the sound is less garbled and the tone control works :D
There are still a few problems. There is quite a bit of hum and I think there should be much more power and bass coming from the speaker. With the volume turned all the way up it still doesn't have the punch and clarity it should have.

Another problem I have is with the loctal sockets on the 7H7s. I've tried just about everything including replacing one with a brand new ceramic loctal. I think the other one has loose rivets and is not grounding well. If I jimmy things around enough I can get the radio to play but now I can't seem to get the filaments to light on both at the same time. Is it just me or are these sockets problematic? I know there's a certain way to remove and install them. Nothing seems to help.
Ben


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