[Guest]

I am restoring a 690. Looking for an original speaker, but wonder if I find a correct sized one, but different field coil resistance. Can I just add the proper resistor in series and have it work OK? The original field coil is 4300 Ohms, shunted across the B+.
Also I notice that someone replaced the rectifier socket atop a transformer with an octal socket and are using a 5U4 instead of a 5X4. To a collector is this a big negative, or should I go back to the original?

Also would like to communicate with anyone who has/is done a restoration. Need all the tips I can get.

[codefox1]

Other than the pinout, the 5X4G and 5U4G seem to be pretty similar, and either one should work out, same PIV and filament requirements, according to my tube manuals. Both are octal based tubes. If the socket was replaced in the past. probably it developed arcing or physical damage. One point of caution when re-wiring, make sure that the "unused" terminals of the socket are not used for other components not related to the tube itself.

I do know that it is pretty easy to get a 5U4G, (and in fact any 5U4 later versions,) but it might be a little harder to scare up a 5X4.

I would defer on the field coil discussion to others. A resistor of the same value (and 25 watts at least) would preserve the balance of the B+. This is a seriously nice set, wish I had one, so please wait for more discussion before proceeding.

[Doug Houston]

The issue of 5X4 and 5U4 is simple. The high current rectifier, 5Z3 was developed about 1933 or 1934. It amounts to a beefed up 80, with the same 4 pin base. You will find it in some Philco sets, such as the 680, and earlier, the console model 16. It was an RCA tube, and before octal based tubes were made, it was the only high-current receiving rectifier.

With the use of octal based tubes, Philco and Zenith, RCA's fiercest competetors, needed and octal-based 5Z3. Sylvania was the supplier to Philco and Zenith, so they simply put an octal base on a 5Z3, and called it: 5X4. Now, RCA had not as yet, put a new base on the 5Z3, and was not about to use a Sylvania design, so a couple of years later, they finally got around to re-basing the 5Z3. They did so, used a different base connection, and called it 5U4. They did it in ime for Television, and high current power supply applications, and as a result, RCA sold far more 5U4's than Philco and Zenith used. Since the industry was swamped with 5U4, rather than 5X4, RCA's baby won out. You never heard of the 5X4 in new equipment after 1938. Note also,that Sylvania re-based the 80 and called it 5Y4. RCA did the same thing, and called it 5Y3.

Now, if you'd want to make the set use either 5Y3 or 5Y4, or use either 5U4 and 5X4, the socket can be wired for the base connections of both 5Y4/5Y3 or 5X4/5U4. I haven't a tube chart handy here, but a quick look at the two base connections will tell you which pins to connect together, to have the socket take either tube. I've done it several times

On the issue of the 14 inch speaker, it may be possible to simply use a PM dynamic speaker on the set if the load of the field on the power supply is not critical. That's something that you'd need to research. I've never investigated it, but I wonder if all of Philco's type "W" speakers have the same field winding?
I had seen one or two on eBay, so hope still springs for you. Remember that, when the big Philcos were being built, the strong magnetic materials were not yet developed. There were Alnico magnets, but not Alnico 5, until just in time for WW II. That's why a lot of speakers with high resistance EM fields were used prior to 1942.

[Steve D]

If you wire the socket to accept dual pin basings, one thing to be careful with is the pin spacing. For the 5Y3/5Y4 for example, if you connect pins 3-4, 5-6, and 2-7 to make it work for both basings then there is only one pin gap between the plate voltage and the filament voltage. Normally there is two pin spacings (blank pin between them) which provides twice the tracking distance.

In older sockets this can lead to carbonization and breakdown. If you decide to do this I would recommend replacing the socket with a modern insulation type which can better withstand the voltage gradients.

Steve D

[Arran]

With the use of octal based tubes, Philco and Zenith, RCA's fiercest competetors, needed and octal-based 5Z3. Sylvania was the supplier to Philco and Zenith, so they simply put an octal base on a 5Z3, and called it: 5X4. Now, RCA had not as yet, put a new base on the 5Z3, and was not about to use a Sylvania design, so a couple of years later, they finally got around to re-basing the 5Z3. They did so, used a different base connection, and called it 5U4. They did it in ime for Television, and high current power supply applications, and as a result, RCA sold far more 5U4's than Philco and Zenith used. Since the industry was swamped with 5U4, rather than 5X4, RCA's baby won out. You never heard of the 5X4 in new equipment after 1938. Note also,that Sylvania re-based the 80 and called it 5Y4. RCA did the same thing, and called it 5Y3.

Are you sure that you don't have that the other way around? More often then not RCA sets I have run across seem to have used the 5Y4, I haven't see the 5Y3 used in very many pre war sets of any brand but I can only comment on the Canadian produced sets. The CGE and Canadian Westinghouse sets also used 5Y4s, although I have a Westinghouse set that used a 5Z4. There is a type up here called a 2X3 that works out to exactly 1/2 of a 5Y3 in pin out and electrically, but this was a Rogers tube only used in Rogers, Canadian Majestic, and Deforest Crosley sets from about 1937-39. Rogers used a pair of these 2X3s in most sets during that period, before that they used 80s and in 1940 they went back to using 80s.
[/quote]
Now, if you'd want to make the set use either 5Y3 or 5Y4, or use either 5U4 and 5X4, the socket can be wired for the base connections of both 5Y4/5Y3 or 5X4/5U4. I haven't a tube chart handy here, but a quick look at the two base connections will tell you which pins to connect together, to have the socket take either tube. I've done it several times
.[/quote]
The same conversion with the jumpers also works for substituting a 5Z4 with a 5Y4 or 5Y3, dig out the tube manual first. I wasn't aware that the 38-690 used a rectifier tube on top of the power transformer, I figured that with two chassis they would have had the space to install a normal chassis mounted socket.
Best Regards
Arran

[Fred R]

Hey Doug,

Don't forget the two top of the line 1942 Philcos 42-1015 and 42-1016 both used 5X4 as rectifiers. So did the 12 tube 1942 Zeniths with FM. I have a '42 Zenith in my cubicle at work, a 12H689 with a 5X4 in it. (It has a home brew converter to play modern FM on it. Sorry, it's not a Philco.)

FR

[FStephenMasek]

I replaced the 2,500 ohm field coil speaker in a little 4-tube TRF with a 1,500 ohm speaker in series with a 1,000 ohm resistor, and it works fine. There is a discussion of this on the Antique Radios Forum, and one guy there has a 450 ohm speaker on his bench for testing, and just uses different series resistors to match it to the particular set he is testing.

You are fortunate to have a 38-690.

[Doug Houston]

ARRAN: You and I both need to get our signals straight about which country certain tubes were used. I forget that tubes, such as 5Y4 were used in Canadian radios, by RCA. I think that there were others too, though examples escape me. Apparently, Canadian RCA wasn't as tightly under Sarnoff's heel as the US RCA. While a lot of Canadian RCA sets used he same chassis as those offered to the south, a great lot of them were totally designs that were Canadian RCA only. Quite a few of the Canadian RCA's were a lot better in quality of design than their similar sister sets in the USA.

So, having serviced radios since 1944, I have a clear idea about what went on south of Canada, buit the Canadian GE and RCA were different creatures.

[Arran]

ARRAN: You and I both need to get our signals straight about which country certain tubes were used. I forget that tubes, such as 5Y4 were used in Canadian radios, by RCA. I think that there were others too, though examples escape me. Apparently, Canadian RCA wasn't as tightly under Sarnoff's heel as the US RCA. While a lot of Canadian RCA sets used he same chassis as those offered to the south, a great lot of them were totally designs that were Canadian RCA only. Quite a few of the Canadian RCA's were a lot better in quality of design than their similar sister sets in the USA.

So, having serviced radios since 1944, I have a clear idea about what went on south of Canada, buit the Canadian GE and RCA were different creatures.

As I said, I could only comment on the Canadian produced sets. What may explain the use of 5Y4s in Canadian RCAs, if it indeed is unique to Canada, is that in Canada we had company, a sort of patent pool, called Canadian Radio Patents limited that the manufacturers owned shares in and could purchase licenses to employ various circuits and devices in the radios that they produced. Rogers owned many of the patents for AC tubes and power supplies in Canada, RCA owned the Superheterodyne, Regenerative and TRF patents, and other companies like Northern Electric and Canadian Marconi held their own, CRP Ltd. allowed radios to hit the market years sooner through co-operation.
There is also the possibility(but a remote one) that the 5Y4 was preferred over the 5Y3 because the 5Y3 was not approved under the Canadian electrical code prior to the war. For example you won't find any Canadian made AC/DC sets built prior to 1939-40, the small sets prior to then were AC even if there was a similar set with an AC/DC circuit in the US .
Best Regards
Arran

[49Stude63]

I won't jump into the pinout basing issues commentary but the 5X4 is an easy tube to find on ebay and if you are going to restore the radio having a hacked 5U4 sub as a rectifier tube would diminish the value. From Doug's remarks it should be just a matter of putting the wire connections back, I have a 38-690 and it is a nice radio, been lucky enough to gather a few of Philcos higher tube count 38 models.