[glwells]

Any one have experience with whether the AES Hammond PT125C or E is a viable replacement candidate for an open 32-8053 on a 40-180? If my research is correct the input impedance for the 42 tubrs in PP is 10,000 ohms.

Thanks,
Gary
WB9AYD

[John R]

Gary,
The 40-180 uses 41 push pull tubes unless you are subbing 42's? If you use 41's the plate load impedance is closer to 12-14K equivalent to the 6K6. If you use 42's it is 10K equivalent to 6F6's.
Don't have experience with the Hammond subs. Sure others are though and can comment. RCA tube manual shows the 6K6 equivalent to the 41 at 12K. The site "www.radioremembered.org" under 'Determining Output Transformer Impedance' shows 14K for the 6K6 in push pull & 10K for 42's. If you go with 10K then Gary at PTOP may have a Philco 32-7981 which is designed for 42's in push pull at $7.75 but with a $20 minimum. The 32-7981 is the exact audio transformer I am currently replacing in my 41-295 which also had an open primary- common problem.
Best of luck, John

[glwells]

Thanks John! I need to clean my half highs. I meant to say 41's. Great tips. I have an open side to center tap on the primary so I am trying to figure the right impedance. I did recheck based on 41's from radioremembered and I do see now 12k. I think I will give the Hammond replacement a try. Now I have to figure out how to make a 2 meg volume control with a 1 meg tap! I just discovered that that isn't tracking anywhere where it needs to be over the range.....unless I can dismantle it and clean it, we'll see. Thanks again. This 40-180 is open heart surgery with all the guts on the table!

Gary

[Ron Ramirez]

You don't want to use 42 outputs in a 40-180 or similar Philco; I doubt that the power transformer could handle the strain of the extra filament current for very long. (0.7A each 42 tube vs. 0.4 A for each 41)

[glwells]

Thanks Ron. I ordered the Hammond 125E from Radiodaze so we will see how it works. I will set it up for about a 12k impedance for the 41's. Now I have to figure out the tone control as I am confused by the 6meg/400k description on the schematic! I hope both pots are ok after I clean them up since I don't find audio tapers with a 1 meg tap around. Thanks again for the help.

Gary
WB9AYD

[Chuck Schwark]

6 Meg pot with a tap at 440K for connection to the loudness compensation components.
There are four (4) lugs on the part the "normal three in a row and one around the
resistance track.

Chuck

[glwells]

Ah ha! Thanks Chuck, I guess I didn't look close enough around the bottom side to see the tap. I have been doing a detailed inspection of all coils, xfmrs and pots, the critical path items, before I start the cap and resistor process. Going to spend today replacing lots of old rubber wire and rebuilding the dial lite.

Gary

[Ron Ramirez]

Hold the phone, guys.

The tone control only has the usual three terminals. Some Philco schematics, such as the 40-180, draw it as a pot with a 6 meg element, a break, then a 400K element in the same unit. Others draw it as a regular pot, 6 meg. I think the early ones (such as used in some 1940 models) were built with a separation in the element; these will check infinite resistance on your ohmmeter. I think Philco later began to use 6 meg pots with no break in the elements. (Thinking as I type here.)

The 6 meg pots work very well as a tone control, when the associated components are of the correct values. I've modified a couple of my sets (my "Super" 71 and "Super" 89) to use this type of circuit. I really like how it works.

Check your schematic. You will find that tone control only has three terminals - the two end terminals plus the wiper arm, no more.

[glwells]

Makes sense as I just looked for the 4th terminal on the tone control. It isn't there as you stated. Your response eased my concern thinking the tone pot was defective with the break in the middle. It certainly tracked strangely when I did check it with my VTVM. I need to ring out the volume control again to see how the 2 meg follows as that has a 400k tap on the side. Hopefully all is well with it so I can move on to other challenges with this unit. Thankfully the 8 pushbutton switches are all good now and the 7 adjustable coils are also good. Bandswitch functions well. Power xfmr ohms out good. As far as I can tell the IF's and oscillator coils are good. Now the grunt work begins with wire changeouts today.

Thanks again for all your feedback and assistance. I am sure learning from you guys!

Gary

[Chuck Schwark]

Aha! Thanks Ron. I stand/sit/type corrected. ;)
Will not that in my archives.

Chuck