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Philco Console Amp...

This is a capacitor?

Isn't it??
I'm rewiring teh inputs, and one of these guys is on teh volume wiper of each pot,,, looks like one connects to each input.... If it is a cap,,,how do I get teh voltage? Color bands are...white, yellow, violet, black, white... the only cap I didn't replace yet, is .0047,,, Maybe this is it??

Thanks for the help,
Regards,
John
 

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wa2ise said:
That looks like a 47pF cap, which is likely fine, you can reinstall it.



I bought that Tull album when I was in high school... :D
Click to expand...

Thanks, that thing was driving me nuts,,, I'll put em back in
Yep,,, I was in the Navy,,, nothing like a rock flute!!!!!!!!!!!!!!
 
Volume control noise....

You know,,, I've been searching for ground loops, bad caps, out of value resistors,,, and it still hums when teh Volume controls are in certain positions,,,Finally,, it dawned on me,,, this thing has bad VCs!!
Seems its another Philco glitch,, this amp has a clutch drive volume/balance controls, which seem worn out, to me, and, if used separately, to adjust balance, they have way to much play in them, and hum and static, when moved side to side,,, The amp is dead quiet when the VC is in the "right" position....

It is a two meg, ganged pot, with a 2 1/4" long stem,,, where can I look for something like that??? I was going to use 2 separate pots, but, I have a nice, brass faceplate for this guy, that I'd like to use...

Regards,
John
 
Update...

knockbill said:
You know,,, I've been searching for ground loops, bad caps, out of value resistors,,, and it still hums when teh Volume controls are in certain positions,,,Finally,, it dawned on me,,, this thing has bad VCs!!
Seems its another Philco glitch,, this amp has a clutch drive volume/balance controls, which seem worn out, to me, and, if used separately, to adjust balance, they have way to much play in them, and hum and static, when moved side to side,,, The amp is dead quiet when the VC is in the "right" position....

It is a two meg, ganged pot, with a 2 1/4" long stem,,, where can I look for something like that??? I was going to use 2 separate pots, but, I have a nice, brass faceplate for this guy, that I'd like to use...

Regards,
John
Click to expand...

First of all,, Thanks for all the help, I am starting to grasp some of teh theory, I think...
I took out the tone control, and its related circuitry, and replaced the original ganged VC with two separate pots,,, I also replaced the 12AX7 with a 7025, I had in a Maggy chassis,,, the sound from this little amp is really nice, much more bass than the Zenith, which is similar,,, but this amp has the separate feedback windings on the OPT's, which I think give it more range...

It still has a little hum, at highest volume, but I'll keep tweeking it, until its gone...

Rergards,
John
 

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That looks very nice
attachment.php

As for the hum that's still left over, maybe a little more shielding of the input wires and the wire that goes from the volume controls center wiper. Did you put a metal plate to cover the bottom of teh chassis? That might help.
 
wa2ise said:
That looks very nice
attachment.php

As for the hum that's still left over, maybe a little more shielding of the input wires and the wire that goes from the volume controls center wiper. Did you put a metal plate to cover the bottom of teh chassis? That might help.
Click to expand...

Thank you,,, I actually sounds better than it looks! It really needs black or brass knobs,,,I appreciate all your help...
I haven't finished mounting the I/P jacks to the back of the chassis,,,I also need to see the best place to run the input cable,, right now, I have it tied into the pots, no caps,,, but, I think I need a cap, to help protect the TD or CDP,,, I believe you already told me that (.047),,, Also, I was reading its advisable to put a 1M resistor from the input tube grids to ground,,, Does that mean grd to the chassis, or to the floating ground buss, (B-) ?
I'll make a plate to cover the bottom of teh chassis, to try, but I'd like to keep it open, for circulation, as it gets pretty hot,,, actually, teh PT is almost to hot to hold on to.

Here's a pic of teh bottom, so far...

Regards,
John
 
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knockbill said:
Also, I was reading its advisable to put a 1M resistor from the input tube grids to ground,,, Does that mean grd to the chassis, or to the floating ground buss, (B-) ?
I'll make a plate to cover the bottom of the chassis, to try, but I'd like to keep it open, for circulation, as it gets pretty hot,,, actually, the PT is almost to hot to hold on to.
Click to expand...

Ideally the 1M resistors you mentioned should go to the same ground that the cathode resistors of the 12AX7 (7025) go to. A good reason for these resistors is to keep the grids from "floating away" if the pot wipers should lose contact. With these resistors you could have coupling caps between the pot wipers and the grids, the 0.047uF caps would work well there.

You could use wire mesh or sheet metal with lots of holes in it. To screen out hum but let the air in to vent the amp. Just be sure to select material that won't get bent inwards to prevent it from shorting out something underneath.
 
wa2ise said:
Ideally the 1M resistors you mentioned should go to the same ground that the cathode resistors of the 12AX7 (7025) go to. A good reason for these resistors is to keep the grids from "floating away" if the pot wipers should lose contact. With these resistors you could have coupling caps between the pot wipers and the grids, the 0.047uF caps would work well there. "

You could use wire mesh or sheet metal with lots of holes in it. To screen out hum but let the air in to vent the amp. Just be sure to select material that won't get bent inwards to prevent it from shorting out something underneath.
Click to expand...

OK,, I can add the 1M resistors, to protect the wipers,,, I understand that...

What would I gain with .047 coupling caps between the wipers and grids? I was reading, the less "stuff" you have in the signal path the better , or I guess, more accurately the music will reproduced,,, that's why I removed R2, R3 and C3, C4,,, it made a big difference removing the tone circuits...
I did put the .047 caps back between the input jacks and the VC...


OK,,, I have some expanded metal that would work for the bottom...However, I think the hum/noise problem, is one of my "design deficiencies" ,,, as, its only present in about 30-40 degrees of VC rotation,, It starts at about 2/3 volume, and is gone a little before full volume... Could it be the wrong type of cap, allowing some kind of frequency through... I did replace the original volume pots, and this noise still slightly appears at the same place in the rotation... I replaced C5 (100uF 3V, polarized, wax/paper cap), with a lytic,,, should I use a different type of cap there?

Regards,
John
 
Long overdue update.....

wa2ise said:
That looks very nice
attachment.php

As for the hum that's still left over, maybe a little more shielding of the input wires and the wire that goes from the volume controls center wiper.
Click to expand...

Finally found the source of the remaining hum, today,,, Little drip of solder, barely touching a cap lead under it... Can't hear any hum, within 6" of speakers....
Gotta get stronger glasses, I guess!! Had it playing all afternoon,,, sounds amazing, for what it is...

Regards,
John
 
Cool. Gotta love it when it ends up being a simple fix. Annoyingly, those 30 second fixes seem to require 30 hours of diagnostics first.
 
gadget73 said:
Cool. Gotta love it when it ends up being a simple fix. Annoyingly, those 30 second fixes seem to require 30 hours of diagnostics first.
Click to expand...

You ain't kiddin'!!!

I had it in the shop, to steal/swap the 3A inrush protector, with a 2A ..., to use on the Maggymoto, and finally saw the drip!...

Hard to believe how good this little guy sounds...

Regards,
John
 
Thanks,,,
An early effort! Got some nice tubes in it now, Pair of NOS Sylvanias, and an Electro Harminix 12AX7....

Regards,
John
 
Here's teh last iteration,,, IT got way too hot buried under teh top cover, so I made a perforated metal top for it, nice and cool now...
 

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I know its been a while since you posted in this but do you happen to have an updated schematic of this little amp? I would like to try and build a small "line voltage" amp like this with the iso transformer as I have the parts laying around. Thanks!

Justin
 
I didn't keep updating the schem as I modified it,,, now it has a pair of 50C5s, 12AX7,,, with SS B+ and filaments on an ISO tx,,, I found a 150v/6.3v PT, so I'm going to swap it over to 6CU5s next iteration, I believe...
 
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