Philco Console Amp...

[knockbill]

Hi Guys,,,

I missed teh SS Fisher console yesterday,,, so, I went to a Hamfest, this morning, and found this little Philco amp,,,But, its a tube amp, so I'd rather work on this... ( after a little searching, it looks like it might have come out of a suitcase phono)

It has a hot chassis, so, I am going to put a power transformer on it... It has a 35W4, 12AX7, and 2x 35C5 power tubes...So, it seems its a little less power output than teh Zenith....

This amp has a stereo-mono switch,,, does that change teh amp from SE to PP? The OPT's have 4 wires on the primary sides of each, maybe a feedback loop?

I have to search for a schematic,,, I don't know if I'll modify this one, or just rebuild it as original...

The chassis is stamped 1410 and 0001077950, (I think, it was stamped twice, and neither are clear)...

Any thoughts?

Regards,
John

 

[Shadowdog]

SE is single ended and runs as a class A amp which you have there with one Output Tube per channel. Maybe 1 Watt or 2 of clean power, by the size of the tubes and low voltages used.

PP uses completely different Output Transformers and usually starts to run out of class A at a certain point as you tun the volume up it goes into class AB. It became popular early on due to it's much greater efficiency, so much more power output.

But SE has it fans in recent years , because of it's merits. It may sound sweet if recapped with the right speakers!

 

[wa2ise]

You'll want to use an isolation transformer, and you might as well replace the 35C5s with 50C5s (a little more output power) and use a bridge rectifier. You'll get a higher B+, which will give you a little more power as well. I'd put the 12AX7 heater between the 50C5s and bypass the 12AX7 pin 9 to ground. You'll see approx half the B+ voltage DC at this point, which makes for less hum from the heater.
The chassis looks plenty big to mount the isolation transformer.

Or if you have a power transformer with 6.3VAC 4A heater winding, and centertapped 250VAC capable of supplying 100ma once rectified full wave, you could use 6CU5s (the 6V heater version of 50C5) for outputs, and a 6X4 rectifier tube.

Replace all the wax paper caps, and the electrolytics.

 

[jaymanaa]

Excellent first time project. :thmbsp: I bet you will be surprised how good it will sound on some efficient speakers (98 or better).

 

[knockbill]

SE is single ended and runs as a class A amp which you have there with one Output Tube per channel. Maybe 1 Watt or 2 of clean power, by the size of the tubes and low voltages used.

PP uses completely different Output Transformers and usually starts to run out of class A at a certain point as you tun the volume up it goes into class AB. It became popular early on due to it's much greater efficiency, so much more power output.

But SE has it fans in recent years , because of it's merits. It may sound sweet if recapped with the right speakers!

Thanks for replying...
This one only has 1.5W, with the output tubes its using, in stereo,,, I'm not sure what the mono switch does to teh power output....

Thats why I mentioned teh 4 primary wires on teh OPT's,, these transformers don't look like the small ones I've seen on small amps, and AA5 radios...

Yep,, my little Zenith sounds great, for what it is,,, and, if I can't find a schematic for this Philco,,, I'll modify it to use different output tubes, (50C5's maybe),, and a SS rectifier, with an IT built into a nice power supply I got from forum member, after I rebuilt the Zenith,,, then better OPT's.... Never ends, does it?????

Regards,
John

 

[jaymanaa]

6AQ5 might be a good output tube to try as well.

 

[Shadowdog]

You mentioned in 4 wires in the primary at first. If they are in the secondary it's probably different ohm secondarys which is common so you can hook up just about any speaker.

6AQ5 or similar 6V6 , but only if you add a regular PS for the higher voltages needed to run them and you would need the right filament voltage, so I don't think plug & play.

 

[knockbill]

You'll want to use an isolation transformer, and you might as well replace the 35C5s with 50C5s (a little more output power) and use a bridge rectifier. You'll get a higher B+, which will give you a little more power as well. I'd put the 12AX7 heater between the 50C5s and bypass the 12AX7 pin 9 to ground. You'll see approx half the B+ voltage DC at this point, which makes for less hum from the heater.
The chassis looks plenty big to mount the isolation transformer.

Or if you have a power transformer with 6.3VAC 4A heater winding, and centertapped 250VAC capable of supplying 100ma once rectified full wave, you could use 6CU5s (the 6V heater version of 50C5) for outputs, and a 6X4 rectifier tube.

Replace all the wax paper caps, and the electrolytics.

Hi Mr Wise...

We were typing at teh same time,,, I wanted to use your power supply ever since I built teh little Zenith,,, I've been looking for a chassis to use it with, and, since I can't find a schematic, for this Philco,, Yet,,, That would be my plan... the 50C5 has almost a watt more power than these 35C5's...

Thanks for replying, as I wanted to give you credit for teh PS... I think this chassis will fit the power transformer easily...

So now,, you gave me more options!!!!!!!!! If I go with 6CU5's what will I gain, as they have teh same output as teh 50C5's,, and I have some of them....

OK guys,, let me hear all your mods, before I work on this thing,,,It really needs caps bad,,, lots of static, but, I could get a signal thru it with a tape deck, but not very well...

I really appreciate all teh help I've gotten on this forum... trying to learn all I can...

Regards,
John

 

[knockbill]

Excellent first time project. :thmbsp: I bet you will be surprised how good it will sound on some efficient speakers (98 or better).

Hey Jay,,
Thanks for replying.... This will actually be my second take at these "dangerous" amps!!! the Zenith was 1.0,,, this Philco will be 2.0...

I got so much help and ideas here, and, I want to try some of teh other mods I didn't get to try 1st time around...

You can't imagine how good that little Zenith sounds, I tuned it for Pink Floyd!!!! The feedback loop killed teh distortion, and the big caps filtered out just about all teh hum...

Regards,
Johbn

 

[knockbill]

6AQ5 might be a good output tube to try as well.

Funny you should mention them,,, I picked up an old RCA Receiving tube manual today,, and I have a box full of 6AQ5's from a stash a buddy gave me...

I just looked them up,, and there would be more power using them,, however, what other mods would I need to do, to benifit from the 6AQ5's,,like different OPT's, etc??

Regards,
John

 

[knockbill]

You mentioned in 4 wires in the primary at first. If they are in the secondary it's probably different ohm secondarys which is common so you can hook up just about any speaker.

6AQ5 or similar 6V6 , but only if you add a regular PS for the higher voltages needed to run them and you would need the right filament voltage, so I don't think plug & play.

Thanks for picking that up I did mean primaries,, and corrected it...

You are right,, teh original plan was using 50C5's, but with the SS power supply, and maybe better OPT"s... I tried to find a schematic to post, but teh Philco number comes up as a TV set....

Regards,
John

 

[RWood]

Hi John,

Glad you found something to fool around with. This one was made on Filbert St, around 10 miles from where you are now!

Here's a page showing the phono:

http://www.philcoradio.com/gallery/1960.htm#o


and here is the schem, attached. I like what Wa2ise has drawn though.

This does show where your OT secondaries go.

 

[knockbill]

Hi John,

Glad you found something to fool around with. This one was made on Filbert St, around 10 miles from where you are now!

Here's a page showing the phono:

http://www.philcoradio.com/gallery/1960.htm#o


and here is the schem, attached. I like what Wa2ise has drawn though.

This does show where your OT secondaries go.

Hi Dick,
Thanks!!!

I figured you'd come up with a schematic,,, I'm going to print it out and study it... Did you read teh whole thread? Seems the consensus is to use the SS PS,, and change teh 35C5's to 50C5's,,, I don't know how teh OPT's will affect teh plans, tho... I would guess teh resistors, and caps will have to be re-sized for the 50C5 tube...

Why does this OPT have so many primaries? I guess it will make it harder to upgrade teh output transformers, if I get that far...

Yep, I'm well aware of Philco,,, My buddy is a big Philadelphia Storage Battery Co, antique radio collector,,, he gave me a couple 1940's radios that I recapped,, but I like teh audio/stereo stuff better than old radios...

Keep in touch,,, I'm sure I'll have a lot more questions...

Regards,
John

 

[Tom Bavis]

6AS5, 6CA5, 6EH5 are other possibilities if you go with a 6V heater winding. 6AQ65 likes higher voltage and would need a 6K or so transformer, versus the 2-2.5K one that's in there now. you could also use a 125V transformer with a full-wave bridge, and a separate 6V / 3A transformer for heaters.

Second secondary on the transformers is for negative feedback. Using a separate winding keeps the speaker wires isolated from line voltage... of course a POWER transformer would do that too, but that costs MONEY...

 

[knockbill]

6AS5, 6CA5, 6EH5 are other possibilities if you go with a 6V heater winding. 6AQ65 likes higher voltage and would need a 6K or so transformer, versus the 2-2.5K one that's in there now. you could also use a 125V transformer with a full-wave bridge, and a separate 6V / 3A transformer for heaters.

Second secondary on the transformers is for negative feedback. Using a separate winding keeps the speaker wires isolated from line voltage... of course a POWER transformer would do that too, but that costs MONEY...

Thanks for teh reply, Tom,,,,
I have been studying teh schematic, and I thought that looked like a NFB loop,,,,

What do you think about replacing the rectifier tube in this chassis, with a bridge,,, and adding the 50C5's instead of teh 35C5's in it now?? It looks like teh pinouts are teh same,, I'm not sure about changing teh resistor and cap values,, however the voltages are similar to teh Zenith chassis I rebuilt...

I still have some 6AQ5 tubes that I'd like to use for a new amp, rather than modify this chassis that much,,,

Regards,
John

 

[wa2ise]

So now,, you gave me more options!!!!!!!!! If I go with 6CU5's what will I gain, as they have the same output as the 50C5's,, and I have some of them....



Regards,
John

Looks like, aside from the heaters, the 6CU5 is the same as a 50C5. Only advantage would be if you had a power transformer that has a 4A 6.3V secondary, along with a centertapped high voltage secondary for the B+.

One reason for the bridge rectifier is to avoid a DC bias happening in the isolation transformer, and less ripple for the same capaciters.

 

[knockbill]

Looks like, aside from the heaters, the 6CU5 is the same as a 50C5. Only advantage would be if you had a power transformer that has a 4A 6.3V secondary, along with a centertapped high voltage secondary for the B+.

One reason for the bridge rectifier is to avoid a DC bias happening in the isolation transformer, and less ripple for the same capaciters.

I want to use your PS with teh full bridge and isolation transformer,,, I assume it can be used as designed for teh Zenith? Do the values of teh resistors and caps apply to this amp also?
Are there any other changes I need to make to convert this amp to the 50C5's...

Thanks for your help,
Regards,
John

 

[knockbill]

1st update....

I cut out the multi cap, and clipped in a few new ones,,, got good sound from it,,, (Blind Faith, may as well bring it up right!!!) next, I'll check voltages against teh schematic... and breadboard the new PS, and 50C5 tubes...

No sense recapping it, until I see if teh new tubes need different values.. I have some reading and experimenting to do!!!!.

Regards,
John

 

[wa2ise]

I want to use your PS with the full bridge and isolation transformer,,, I assume it can be used as designed for the Zenith? Do the values of the resistors and caps apply to this amp also?
Are there any other changes I need to make to convert this amp to the 50C5's...

I'd change the 120 ohm resistors in the cathodes of the output tubes (to become 50C5s) to 150 ohms. Other than that, all other resistors can stay the same. And replace the wax caps with the same values.

 

[knockbill]

I'd change the 120 ohm resistors in the cathodes of the output tubes (to become 50C5s) to 150 ohms. Other than that, all other resistors can stay the same. And replace the wax caps with the same values.

Thanks for the reply... I will change teh 50C5 K resistors, as you noted,,, 150 Ohm is what they are on the Zenith...

Should I use the filter cap values you have drawn on the PS for the Zenith, or use the PS, but connect to the Philco multi cap values? I would probably raise teh capacitance a little,, my goal is to get the amp as clean, and quiet as possible,,,given its limited power ..

Those old Philco caps do look ugly,,, I am making a parts list, as we speak,,, I guess I should get a couple of those IT's if I'm gonna keep fooling with these little amps...

As always, I appreciate your time and help,,,

Regards,
John