Replacing a missing speaker - Printable Version
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+--- Thread: Replacing a missing speaker (/showthread.php?tid=18524)
RE: Replacing a missing speaker - Eric - 07-02-2018
Yesterday was terrible it was one step forward three steps backward! I ended up replacing the volume and tone controls, they were not original as the values were off and they had dead spots so I had some that were close and put them on. I caused a ground to the plate of the 6B6 when I replaced the lead to the grid cap when I had the shield reinstalled a lead was touching the shield but didn't know it and wondered why it is drawing a bit more and I lost all sound? I went this morning and took that IF can apart and saw what happened. Also found a broken solder tab and repaired that. Hooked up the signal generator and I was able the peak both IF's after unhooking the SG I got beautiful static and turned the dial and picked up a station.
I will probably leave it with the one output tube as it plays fine and it is part of the family history.
Thanks Terry and Mike for your help.
RE: Replacing a missing speaker - Eric - 07-10-2018
Probably got a head of my self.
I'm using a 8" ak speaker with a 2k field coil and I added a 500 ohm resistor and that gives me about 150 volts on the plates and the other voltages look good!
One thing I noticed is the volume is not very loud, I have replaced the vol with a newer pot as the old had dead spots in, it had a 150k and the one I put in reads about 170k which I think is ok.
I'm currently using it as I found it meaning using only one of the 41's. Is the weak volume because this. The audio transformer coils check good, and I use a 25' ant in my garage I get a good selection of stations just not enough volume do I need to give it a try and change it back?.
Where to look?
Eric
RE: Replacing a missing speaker - Radioroslyn - 07-10-2018
Hi Eric
I looked over the diagram and something rather curious in that the vol control is list as 2ohms. This is VERY low in resistance and wouldn't be suitable as a vc. Even @ 150K is still fairly low in value and will load the input to the 1st audio stage and the avc circuit. If you happen to have a 500K or 1M I'd give that a try. It could be a misprint on the diagram and it should read 2M rather than 2 ohms, that would make more sense.
GL
RE: Replacing a missing speaker - Eric - 07-10-2018
My mistake the info I posted was for the tone not the Vol. I have a 1.5meg for the volume control as I figured it was a typo. I'm use to seeing the Vol and switch on the same pot and here they are switched.
RE: Replacing a missing speaker - Eric - 07-12-2018
I'm beginning to think the speaker / opt transformer ( using a PT- 291) I'm using the C & 3 taps could be the problem?
Could the use of a single 41 be the problem? Seems they wouldn't do it if it didn't work?
Have tried some different pots on the Vol control and that made no difference.
Also swapped out the 37 tube no difference.
Grasping at straws!
Eric
RE: Replacing a missing speaker - KCMike - 07-12-2018
I'll throw this out not sure if its the problem.
You mentioned that you did not change the by-pass caps in the big can. Part #P-24189.
That can has 10 capacitors in it, and it was a real pain to remove and restuff.
Maybe someone that knows circuits better than me can see if one or more of those caps if bad, could cause your low volume.
RE: Replacing a missing speaker - Eric - 07-12-2018
Mike,
I've done a couple of cans like that and dread doing them ( may have no choice). I've been doing some experiments and I usually stay at the lower end of the band as two strong stations are 680 and 750 so I went up scale and at around 1500 the volume increases so that has me baffled still not as loud as I would expect but better! I'll probably do a set of voltage readings and double check the resistor and cap values, it wouldn't be the first time I transposed a value!
Eric
RE: Replacing a missing speaker - Eric - 07-14-2018
Ok I found my mistake, Resistors R9 250k & R10 1meg are connected at a common point along with Cap C-22 what I did is swap the two other ends. They were located in a tight corner and not easily accessible but my volume is now good. I did the alignment and peaking of 1 & 2 IF's. Even the SW works after some cleaning of the rotary switch. I'll post a picture when I get it together.
Mike
I am curious in your pictures you show a resistor across the tone control mine did not have that nor do the prints show a resistor ?
Eric
RE: Replacing a missing speaker - KCMike - 07-14-2018
https://imgur.com/paKIgwA
Good to hear you got the problem figured out.
That resistor you asked about was there when I first opened up the chassis.
I can only guess that who ever put the philco tone control in thought they needed it.
As you can see by this picture I removed it during rehab.
RE: Replacing a missing speaker - Eric - 07-14-2018
Finished radio.
RE: Replacing a missing speaker - KCMike - 07-14-2018
Very nice radio
... and it has the knobs that are so often missing.