October 22, 2019 at 10:23 am #12101
I have had a GE ‘lowboy’ in my collection for many years. The previous owner did a reasonable job restoring the cabinet, but had not touched the chassis. I finally decided to refurbish the chassis.
Unfortunately all labels and identification markings are missing from the chassis and cabinet. Prior to removing the chassis from the cabinet, it appeared to be an 8 tube set, and I found a close match to the cabinet style on radiomuseum.org – a GE Junior S22 (R7 chassis), which it resembles (visually) very closely. However, when I removed the chassis I noticed that there was a tube missing, making it a 9 tube chassis. The tube complement of the chassis I have, as found, is 3 x 24A, 3 x 27 (one missing), 2 x 45, 1 x 80. The ‘extra’ (missing) tube has had ‘AVC 27’ scribbled on the chassis next to this tube socket, which is ceramic (all the other tube sockets are phenolic). This, along with how the ‘extra’ tube socket has been installed, adjacent/over other chassis cut-outs (see photos), suggests that this may be a modification to an R7 chassis. If so, it has been done with some skill. Type 24A tubes could have been substituted for the two 35’s in the R7 design (RF and IF amplifiers) as Type 24A is a sharp cutoff tube and Type 35 is a remote cut off tube, with otherwise similar specs (so would likely work ok as no AVC is included in the R7 chassis). I would welcome any thoughts and suggestions as to what GE chassis I have here so I can obtain a schematic. In the meantime I will start to investigate how the ‘extra’ 27 tube is wired into the circuit. Thanks!
Attachments:October 22, 2019 at 12:58 pm #12114
I am now convinced that someone had added that tube socket: the heater connections (pins 1 and 2) have been connected to the heater connections of the adjacent RF amplifier tube socket, the cathode (pin 4) is not connected to anything and the plate and grid (pins 2 and 3) have been connected together but not to anything else – go figure! So I think this is very likely an 8-tube R7 chassis after all (but with 24A tubes subbed for the 35s). The investigation continues…October 22, 2019 at 1:15 pm #12115Sterling SpurrellCVRS Member
It looks like a r-7 chassis.October 22, 2019 at 2:17 pm #12117
Thanks for the confirmation Sterling – that’s what I think too – unfortunately its been ‘got at’… At least the transformers check out ok, so I will go ahead and work on it.October 22, 2019 at 3:32 pm #12118Sterling SpurrellCVRS Member
It could be GE S-22 chassis also which is very close to r-7 chassis.October 22, 2019 at 4:23 pm #12119
What is the difference between the S22 and R7?October 22, 2019 at 6:52 pm #12120Bruce MorgensternCVRS Member
I don’t know if this will help or not. This info came out of the “RCA Victor Service Manual Volume I” Pre 1939. It does not show a S22 but does show a R22 which I have also attached sheets for. RCA does not show alignment procedures for each individual model but at the end of the manual there are nine pages of alignment procedure. If you would like them I could scan them and send them to you..
Hope this might be of some help.
Attachments:October 22, 2019 at 7:00 pm #12125Bruce MorgensternCVRS Member
One page did not go as it was too large. Here is a smaller size of the page.
Attachments:October 23, 2019 at 8:39 am #12127Ed KrausharCVRS Member
The chassis looks very much like a CGE S22 type. I have just finished restoring a basket case one. It has one 24A and two 35/51s and would probably work with all 24A’s.
What is interesting is years past I had purchased two different radios but of a similar age and tube complement. Both turned out to have been modified to add a type 27 tube, probably for AVC. The work was well done and typical of a local repair person. I did not get further into the mods as I was only interested in original chassis to restore without mods to the steel chassis and moved them on. I guess your chassis had the same fate.
Ed.October 23, 2019 at 10:51 am #12128
Thanks Bruce and Ed. I think what I have here is a modified R7 chassis – that socket marked ‘AVC 27’ sounds very similar to what you found on your chassis Ed, though either the mod was partly reversed, or was never completed. The two 45s in the output stage of the chassis I have here definitely rule out the R7A chassis (the R7A has 47s in their place). Of course AVC would not have worked properly anyway with 24As installed in the chassis in place of 35s. I found the chassis layout diagram in Riders (photo attached, along with underside view of the chassis I have). There seems to be some other mods as well – note the large green resistor hanging off the resistor board near the tuning gang. I will report back when I have taken a closer look to see if there were any changes made to the grid circuits of the RF and IF amps for AVC control, and what that large green bodied resistor is doing…. what a ‘rats nest’ of a chassis.
- This reply was modified 11 months, 1 week ago by Gerry O'Hara.
- This reply was modified 11 months, 1 week ago by Gerry O'Hara.
Attachments:October 23, 2019 at 11:00 am #12133
Sorry there are two photos of the under-chassis view – I was trying to load one with the same orientation as the diagram, but it always seems to rotate the wrong way! (and I can’t find a way of deleting one of the ones I have uploaded).October 23, 2019 at 11:35 am #12135Ed KrausharCVRS Member
That mod reminds me of a local friend from some years back. He repaired radios and I could usually tell when he had worked on one that I acquired. He had good knowledge but being the repair end of the business repaired or replaced or modified only that which was necessary to get the radio playing. Your chassis brought him to mind as typical of his work.
Interestingly he moved from Ontario to BC, somewhere north of Nanimo to continue his business there. I understand he passed away about 5 years ago.
You will find that the capacitor box is a bear to get out and the wire from it go all over.
Perhaps this site may help a little–
Ed.October 23, 2019 at 3:14 pm #12136
Thanks for the link Ed – I will take a look. Seems like the IF cans have to come out to access the base of the cap can. I have done a few of these types before on other chassis – I really dislike the tar smell and mess! On some sets, usually for other folks that are not bothered about under-chassis cosmetics, I have bottled out and just installed caps were the wires connect to under the chassis – works, but can look a bit messy.November 2, 2019 at 9:03 pm #12211
I finished recapping this chassis (without re-stuffing the bypass cap can), and used the additional tube socket as a speaker socket (instead of the captive speaker wiring). Unfortunately the primary of the RF/Mixer transformer was burned out and no voltage was getting to the RF tube plate. I gave up trying to repair the burned out winding (after a long time trying), and so I ‘kludged’ it, using an RF choke (3.5mH), a resistor (1.5Kohms) and coupling capacitor (56pF) and all is now well. A copy of the schematic with this kludge sketched on, as well as the previous mod to the local oscillator bias arrangement is attached to this post. This kludge technique is remarkably effective for cases where a transformer winding is burned out (RF, IF and some AF situations. See this link for IF and AF solutions). The chassis is back in the cabinet and it sounds great!
- This reply was modified 10 months, 3 weeks ago by Gerry O'Hara.
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