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I've been poaching 660L - Printable Version

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I've been poaching 660L - Radioroslyn - 09-29-2013

Well this started about 2:30am this morning. I got up and by 3am I was headed north. Normally I wouldn't make this long of a drive but thought this set would be an exception. It was up in the Boston burbs which is about five hrs each way. The set is a Philco 660L https://philcoradio.com/gallery2/1936a/#Model_660L
I've never seen one in the flesh. It's a odd cabinet with a door on the top that spring loaded, flips up when you push the round molding in the center top of the cabinet. The printing on dial is facing backwards and the dial is up side down.
The radio itself sports a ten watt P/P class A output stage, two IF amps, and a RF amp. Covers LW 150-390kc,AMBCB,and two SW bands 1.750-18mc. Should be a real humdinger when I get it working.
The cabinet is pretty good, the top has a LOT of scratches and will need to be refinished. The rest is not too bad except for a small piece of missing molding and a few chips here and there.
Anyway I met the seller at 7:30am and bought it. The price was very good too. I'm sure I spent more on tolls than on the radio. Hit the front door of my house at 1:06pm. Will unload it and get some pics of it on my flicker page. I know Ron will want one for the Gallery and I picked up a 42-854T (a nice sturdy portable w/sw) for the Gallery too. http://www.philcoradio.com/gallery/1942a.htm#am
Terry
ps Here's some pics. http://www.flickr.com/photos/53710524@N06/10005211523/in/photostream/

RE: I've been poaching 660L - sam - 09-29-2013

looks nice wide but nice lets see open 8)

RE: I've been poaching 660L - Radioroslyn - 09-29-2013

http://www.flickr.com/photos/53710524@N06/10005147296/in/photostream/
Use arrows on each side of pics to see more.
Terry

RE: I've been poaching 660L - Ron Ramirez - 09-29-2013

Great acquisition! Icon_thumbup

Is that 660L as heavy as it looks?

RE: I've been poaching 660L - Radioroslyn - 09-29-2013

Not too heavy but big! Weighs about half as much as that AK-53. Feel free snag any of those pics.
Terry

RE: I've been poaching 660L - Ron Ramirez - 09-29-2013

Thanks very much, I will...after the move is complete...

RE: I've been poaching 660L - Jamie - 09-29-2013

Good score! That's a nice one!

RE: I've been poaching 660L - Mondial - 09-29-2013

Congratulations, that should be a great sounding radio.

I have been working on a model 118B with the same "super class A" push pull triode connected 42 output stage, and am quite impressed with the audio quality. The difference is immediately noticeable compared to my other similar radios with pentode connected 42's.

There really is something special about a well designed P-P triode power amp.

RE: I've been poaching 660L - Gene Pederson - 09-30-2013

Nice acquisition of an unusual Philco O hunter of the nightIcon_e_wink

Gene

RE: I've been poaching 660L - TA Forbes - 09-30-2013

The 118 is an excellent sounding set for an 8-tuber. You get a 10-watt table set or console, which is pretty good!!

Terry, the 660 is a great find!!

RE: I've been poaching 660L - Radioroslyn - 09-30-2013

Tnx for all the kind words guys. After looking it over in the daylight, in Beantown it was foggy the finish is pretty shot will need to refinish the whole to make it a good looker. Will be a good winter project.
Here at the house we have been doing some renovating alot of concrete and rebuild a bathroom. Trying to get the basement a bit dryer. Anyway I've been sidetracked from doing radio work.
The good news is I've got to cleanup some stuff so I'll have some freebees for anyone who wants them mostly parts.
Terry

RE: I've been poaching 660L - Arran - 09-30-2013

It has the power output #42s tubes wired in as tetrodes, not triodes, the screen and plate maybe connected together but they still have a suppressor grid. In fact they can't be wired in as triodes because the suppressor grid is internally connected to the cathode. The power output stage is different in the 660 compared to the 118 in at least one way, in the 118 the type #42 driver is wired up as a pentode with the screen connected through a .006 uf capacitor to ground, in the 660 it's connected as a tetrode, with the plate and screen connected together, just like the output tubes.
Regards
Arran

RE: I've been poaching 660L - Mondial - 09-30-2013

Arran, there is a mistake on the 118 schematic. In the actual radio the driver plate and screen are connected together and the .006 uF cap connects to both, with the other end to ground.

Althhough the suppressor grid remains connected, the tube with the plate and screen connected together still acts as a low mu triode. The tube data sheet refers to it as triode connection and the characteristic curves shown reflect that condition.

http://frank.pocnet.net/sheets/093/4/42.pdf

RE: I've been poaching 660L - Arran - 10-01-2013

It should perform better then a pair of straight triodes as the suppressor grid will eliminate the secondary emission problem. I'm not surprised about the error on the 118 schematic, it doesn't make much sense have a screen grid connected in that manner, sort of just sitting there with no B+ on it. I guess the purpose of the .006 uf cap is for tone correction, since it isn't present on the 660. I have a Canadian Philco 3118B, and finally got a replacement speaker for it, so I have a little more motivation to get it going. Like most 18s and 118s the 6500 ohm bleeder resistor has failed, I think it needs a 20 watter as a replacement, but I only have a 10.
Regards
Arran

RE: I've been poaching 660L - Mondial - 10-01-2013

There is also another error on the 118 schematic. If you look closely, the screen grids of the 78 RF and 78 IF tubes are connected together with no source of B+. In the actual set, the screens of the 78's and the 6A7 are all connected together and obtain B+ from the voltage divider resistors 67 and 68, which are bypassed by the 2 uF electrolytic 46. It appears there is a dot missing on the schematic where the two perpendicular lines cross.

Yes, it seems that the 42 can operate with very good triode characteristics. Looking at the data sheet, a pair in push pull can deliver up to 13 watts with only 2% distortion. Compare that to a single pentode 42 output which only puts out about 3 watts with 8% distortion.