[Ron Ramirez]

Model 400 was introduced in the fall of 1963 as a 1964 model, along with the then-new 500-C and 800-C. The 400 was sort of a stripped-down 500-C, an "entry level" stereo receiver compared to its bigger brothers, the 500-C and 800-C.

It is unusual in that it uses four oddball magnoval audio output tubes, the 7868.

I found mine in May 2016 at Kutztown. Here's a picture I took of it as soon as I brought it home.

[Image: http://www.philcoradio.com/images/phorum...00_001.jpg]

Since I took that photo, I have replaced the two missing brass knob brights, but had not done anything else to it. In spite of knowing better, I did try it out with headphones...and was thrilled to discover that it worked!

Did you notice something wrong just to the left of the headphone jack, just left of lower center?

Here's a closer look:

[Image: http://www.philcoradio.com/images/phorum...00_002.jpg]

And a look inside at the same broken switches:

[Image: http://www.philcoradio.com/images/phorum...00_003.jpg]

So the challenge was...what to do about those broken switches?

[Ron Ramirez]

Well, I could have spent big buck$$ on authentic 400/500-B/500-C/800-B/800-C pulls from the auction site...

..but as Red Green has said so often, "I've got a better way."

[Image: http://www.philcoradio.com/images/phorum...00_004.jpg]

This is a 1969-ish Fisher 175-T solid state receiver. Notice those four slide switches on the right?

[Image: http://www.philcoradio.com/images/phorum...00_005.jpg]

I decided that since I had the junker chassis, I would utilize two of its switches in the 400. They are all DPDT, just like the 400 switches. They are the same size as the original 400 switches. Their outward appearance is the same as the original 400 switches. There was one difference, however...

[Image: http://www.philcoradio.com/images/phorum...00_006.jpg]

...the 175 switches do not have solder lugs - they utilize push-on terminals.

A better look:

[Image: http://www.philcoradio.com/images/phorum...00_007.jpg]

Other than the connections on the back, they are identical to the original 400 slide switches.

[Ron Ramirez]

I carefully unsoldered all of the connections from the two broken switches, replacing one switch at a time. I then made lots of splices and utilized those push-on connectors in the 400 as you can see below.

[Image: http://www.philcoradio.com/images/phorum...00_008.jpg]

[Ron Ramirez]

While I had the face plate off, I also replaced the original fuse lamps with LED lamps.

Once I finished installing the replacement switches, I put the face plate back on, hooked up a pair of speakers, and tried it out.

It sounded great...

[Image: http://www.philcoradio.com/images/phorum...00_009.jpg]

Here's another look, with the overhead workbench light turned off:

[Image: http://www.philcoradio.com/images/phorum...00_010.jpg]

It looks much better with the Fisher 175 switches in place of the broken switches.

And if anyone looked at this receiver from the outside, they would never know that two of its slide switches came from a Fisher 175-T solid state receiver. All of the switches look identical. And the replacement switches function the same as the originals.

No, I am not finished with this receiver yet. For safety, reliability and longevity, I'll be replacing its electrolytic capacitors and rectifiers. I plan to do that in the near future.

I liked the Hayseed Hamfest electrolytics in my TA-600 so much that I plan to use them again in this 400 (and, this winter, in a 500-B I bought in April).

When I resume working on this 400, I'll likewise resume posting in this thread.

[Arran]

Ron;
  My inclination would have been to dismantle the switches and swap the slides from the ones out of the solid state unit into the ones from the 400 B. Actually with some patience, if you did not already have the junk tuner as a parts donor, you probably could have found either some NOS replacements or salvaged some from another piece of equipment, Hallicrafters S-38s and some other models used the same switches, although I think that they were black, as well as some test equipment from the same era.
Regards
Arran

[Ron Ramirez]

Yes, I suppose I could have done that...but I see nothing wrong with my solution. From the outside, it looks like it has all four of its original switches.

In the past few weeks, I've been distracted from the 400 by restoring my Fisher 202-R AM/FM tuner, circa 1960-61. It had two slide switches in the back, both of which were broken. I did try to rebuild them using new switches (which have black sliders), but the old sliders were not compatible with the new switches and actuators...so I had to totally replace them. And they were riveted in, not screwed in as are the 400 and 175-T switches. That made the job just so much more fun. NOT. I slightly damaged my FM antenna terminal board trying to remove those rivets; I finally succeeded in drilling them out. At least I did not damage any of the silkscreen print next to the switches in back.

[Phlogiston]

Those brown slide switches break a lot more often than the regular black ones. Replacements go for a premium on Pay-Bay.

A lot of my amps use the 7868, just another 6L6 variant in a smaller, hotter bottle. DO NOT plug in any of the Russian replacements. They will ruin the sockets.

[Ron Ramirez]

Those brown slide switches break a lot more often than the regular black ones. Replacements go for a premium on Pay-Bay.

Yes indeed. I consider myself very fortunate to have that 175-T junker chassis. As I see it, it finally proved to be good for something.

You know, if I had to do it over again, I might have tried what Arran suggested. It was probably more work to add those push-on terminals to the 400's wiring than it would have been to switch (no pun intended) the terminal boards, or to put the 175-T switch sliders into the 400 switches. That is, assuming the sliders and actuators were compatible with one another. I've seen two different types of Fisher actuators and they are not compatible with one another.

DO NOT plug in any of the Russian replacements. They will ruin the sockets.

Russ is absolutely right. The pins of the new Electro-Harmonix 7868 tubes are larger than the originals. Once you get them in (and from what I have read, they will go in but it isn't easy the first time due to the larger pins), you are then forever limited to using E-H 7868 tubes in those sockets.

OTOH, if you want new 7868 tubes, you are pretty much limited to using the Electro-Harmonix tubes unless you can stumble across a set of NOS American made 7868s.

[Ron Ramirez]

I forgot to mention...my 7868s seem to be in good shape.

[Arran]

I wonder why the brown slide switches would be more fragile then the black ones? Are the slides made out of a different material, such as polystyrene verses black Bakelite?
  I've run into 7868 tubes before, in the power amp for a Rowe-Ami juke box. I think that they are another one of those tubes that the tube division of RCA developed, sort of a solution to a problem that nobody had. In any event I told my friend with the juke box that if those are shot then it would probably cheaper and easier to replace them with a pair of 6L6s by tossing out the magnoval sockets in favor of octals, or at least by making adapters.
Regards
Arran

[Phlogiston]

Probably true Arron, but in all of the Hi-Fi applications I have seen 7868s, 6L6s will not fit. The 7868s in my Sherwood are even installed at an incline to fit in the small enclosure. I think the point of these tubes was to get 6L6C power in a much smaller space.

I always install a fan on these tubes.

[Arran]

Russ;
  Fortunately, in the case of the Rowe-AMI power amp a 6L6 conversion would probably fit, unlike a tuner-amp there is no cage or lid over the top, and the chassis is fairly large as I can recall, but some measuring might be in order to see if octal sockets might at least fit. Then we might get away with using Russian/Soviet 6P3s or metal 6L6s which are more compact then 6L6Gs/6L6GBs etc.
 EL84/6BQ5s are another winner in the hot running and self destructing tube department, (basically a 6V6GT in a small envelope), depending on how hard they are driven. However at least those are 9 pin, and were made, and used, by many manufacturers in many countries, so one has many more options for replacement.
Regards
Arran

[Phlogiston]

The 7189A (6BQ5 variant) is my choice for the audio tube most likely to melt in it's socket.

[Arran]

The 7189 was the choice of power amp tube in that same friend's Magnetone guitar amp. I told him that if those are DOA then were are going to substitute them for 6BQ5s, unless the Russians have an equivalent.
Regards
Arran

[Ron Ramirez]

They do - 6П14П is the equivalent of 6BQ5 or EL84.

6П14П-EB is the equivalent of 7189.