Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

Plate voltage 71A on a model 20
#1

Hello,

hope you can undestand my english Icon_smile

I've recently bought a Philco Moel 20 on ebay. it was in vey bad condition. lot of rust, CV iout of order because of the rust, the main power transformer was burned...

I've rewind the main transformer for the voltage in France so the primary is made for 230V AC. I've renew all the bakelite caps and main block condenser.

The model 20 works good.

I've got a question about the plate voltage of the push of 71A.
If you look at the schematic, you see the point labelled "D". At this point are directly connected the plate of the 24A, le center taps of the primary windind of the output transformer and the coil of the speaker. The service manual say thaht the plate voltage of the 24 is 250VDC. So i suppose there's 250V at the point "D" and also at the center taps of the primary of the output transformer. The manual says that we do have 215V on the plate of the 71A.

I do not understand how is it possible. The resistance of the primayr of the output ttransformer is know enough high to explain the difference of 35V.

And if you look at the datasheet of the 71A, the maximum is 180V on the plate. My question is, why philco have made de decision to put 215V on the plate because it's a little bit high ?

After the rewinding of the main transformer, I've got 330V AC on each HV winding. After the first filter and the first choke, I have 240V DC, (it's not 250V but it's OK, the radio work) What is this mystery ? I don't understand. All the other voltage are OK.

many thank's for the reading (oh.. if you understand one word of course Icon_lol ).

I will made an page on my web site to explain all the works on this model 20 and I will give all the details of the rewinding of the main transformer, because I've count the number of turns of each winding and the diameter of the wires I've used.

I'm very happy to hear it working again.

best regards
Frederic ABGINOLI




Users browsing this thread: 2 Guest(s)
[-]
Recent Posts
trying to identify this wire type
Thanks to all for the feedback. As Arran said, it is probably an older replacement and yes it has a grid cap so I will ...georgetownjohn — 09:32 PM
trying to identify this wire type
It's possible that the red wire, actually a grid cap lead, is a very old replacement, I can't remember seeing a pre 1939...Arran — 09:18 PM
Gilfillan Brothers Car Radio?
Hi everyone,  Special thanks to Joe Rossi for tracking down this obscure radio and thanks to others who took up the hun...Antipodal — 08:15 PM
trying to identify this wire type
Here's one source for your wire of many. Take care and BE HEALTHY! Gary P.S. Can't get the right color you need? I ...GarySP — 06:40 PM
trying to identify this wire type
...and modern wire of the appropriate gauges and insulation V-rating (300V minimum, usually shown right on the wire) is ...morzh — 05:47 PM
1930s Stromberg-Carlson Tombstone Radio need help identifying model number
I have a question about this radio, is there anyone that has access to this radio that has an intact unmolested speaker ...captainclock1988 — 04:28 PM
1930s Stromberg-Carlson Tombstone Radio need help identifying model number
Well what makes me confuse all of those companies is that all three of those companies (Setchell-Carlson, Stromberg-Carl...captainclock1988 — 04:21 PM
trying to identify this wire type
The red wire is rubber covered wire. The others are cotton braid over rubber often in colors or a tracer, also strand...Chas — 02:43 PM
trying to identify this wire type
Greetings Phorum members, Hope you can help me identify this type of wire in the photo I have attached.  I am not sure ...georgetownjohn — 01:53 PM
Philco 60 Squealing
All correct shields must be in place, all tubes correct no subs of any kind. Check any soldered, riveted ground conne...Chas — 01:24 PM

[-]
Who's Online
There are currently no members online.

>