[davemc]

I am starting the restoration of a 37-2670 (Export Model) set. This is a very complex 11-tube set with 5 bands including long wave. But unfortunately it uses the famous 37 RF subchassis. This one is especially packed - no way to get to the bypass caps. I have read all the info I could find on philcoradio.com and the philco repair bench.

It looks like all the wires going to the subchassis can be unsoldered from the MAIN chassis area - they all appear to go to tie points. It then APPEARS that the RF chassis can be removed. Looks like the sides can be removed, which would allow somewhat easier access. I have no done this before.

Does anyone have any previous experience they can share, or point me to other information?

The only major defect I have found so far is the output transformer (open) and of course the Candohm. At least no one has ripped out the bakelite blocks, and the power transformer, choke, speaker field, and even the shadow meter coil are OK.

Thanks for any help,
Dave

[AI2V]

It looks like all the wires going to the subchassis can be unsoldered from the MAIN chassis area - they all appear to go to tie points. It then APPEARS that the RF chassis can be removed. Looks like the sides can be removed, which would allow somewhat easier access. I have no done this before.

***It's not really that difficult to remove the RF chassis. First there's the wires- perhaps 8- just mark them in a sketch. Remove the dial. Next come the screws that hold the right side of the chassis on- once they are removed, the right chassis will swing out an inch so as to clear the RF chassis rubber mounts.

BE VERY CAREFUL WITH THE BAND MASK!!! IT HAS NO PROTECTION ONCE THE RF SECTION IS REMOVED!!

Once you have removed the RF section, you will see that the side covers are held on by screws on the top of the chassis and front and rear. Once the side covers fall off, you have full access.

Not too long ago I had a particularly nasty 37-660 (same chassis) that had been mutilated and miswired, along with RF switch contacts bent outward. It took perhaps 10 removals and installations of the RF section before it worked fully. It took about 20 minutes to remove and install the RF section each time. The end result was worth all effort. A super receiver with great sound. [/b]

[davemc]

Thanks for the help. I was able to remove the RF subchassis (there were 14 wires to unsolder). I removed the side covers, but there are still MANY components that cannot be removed, including several resistors that are +50% high.

So, I am going to have to disassemble the unit to gain access. I ASSUME that the bandswitch shaft can be removed, connections from each section unsoldered, and the whole subassembly removed for service.

I also ASSUME one would not be advised to rotate the bandswitch wafers while they are removed!

I really don't see any other way. This unit is really packed, and I cannot ever SEE some of the parts that need to be changed.

Dave

[AI2V]

You shouldn't have to remove the switch shaft. I didn't and was able to replace all of the bad components but it is difficult. It's not VHF or UHF so the components don't need to be exactly positioned as originally. You can snip out bad parts leaving the leads and making hook joints. Apart from the usual .01's through the 0.1 caps and the big electrolytic, your primary interest should be in the nasty front section; don't worry about the resistor values in the 2nd and 3rd sections unless they are easily replaced.

I could not have done any of this without a high intensity LED light on the end of a length of wire; that simple light allowed me to see all sorts of things otherwise hidden. It's a MUST for servicing this series. Surgical clamps are also a necessity. Also I'm assuming that you have a pencil type soldering iron and not one of those half-loop Wellers.

If your tube sockets look corroded or bad, now is the time to replace them.

[planigan]

davemc, if you do decide to remove the shaft on the band switch it has, or at least mine on a 37-650 did, a keyway on the shaft so the switch position can only go in one way. Be careful though, the keyway is only a small protrusion on the shaft and can be forced on incorrectly if you use too much pressure. The keyway aligns each wafer's rotor correctly on the shaft then the orientation of the shaft itself is oriented by a tab on the front mounting bracket and a hole in the chassis so that the rotors are all aligned properly on the shaft vis a vis each other and then aligned to the proper contacts on the stator. I discovered this by trial and error. Imagine my horror when I smugly replaced the shaft to the keyway but then had two posible positions in which to mount the shaft to the chassis. I actually mounted it 180 out but noticed that the front mount of the shaft would not snug up to the face of the chassis. It was then that I noticed the tab and hole. Check as you disassemble for the keyway and tab. If you can't find them don't remove that shaft! PL

[davemc]

Thanks. I took great care to ensure the the switch sections not be rotated and made notes as to the shaft position. Then I discovered the notch you mentioned when I put it back together! Smart design.

I had no problem removing the three sections of the RF unit for service. There are only a few connections in each section. I really don't see how it would be possible to reach some of the components unless this were done. I was also able to clean out the dust and crud and clean the swith contacts.

I had difficulty removing a couple of bypass caps that were sandwitched between wafers EVEN WITH IT DISASSEMBLED! There was really no way to cut the lead with any tools I have - the coils were in the way. So I just twisted the cap until the lead broke. I was then able to resolder the connection using my Wen 222 "hot shot" soldering gun.

The two resistors in the RF amp section were OK, but the two in the oscillator section needed to be replaced.

I restuffed all the caps in their original cases, as well as the filter cap can.

One worry: the oscillator section has two mica caps that the schematic says are 250pf. One measured 330pf (it was small and had a single yellow dot - blank - yellow - blank (or brown?)). But the other one was larger, had a single center red dot, and measured 2000pf. I left it in place - I wonder if there was a change? These were padder caps.

Dave