Lafayette Comstat 25b

[dime196604]

I been into radios for a few years now i am 27 and just picked up a bunch of vintage stuff the other day. One of the items was a Comstat 25B and i have no experience with vacuum tubes so here we go the radio powers up and works, every tube inside have a slight amber glow with the lights out but one tube glows blue through out the hole tube. is this a sign of the tube going bad? This one tube heats up in like 1 or two minuets so hot that it will burn you if you touch it, and all the other tubes are just warm. Like i said i know nothing about tubes and just need some info here

[TheSpaceMan]

Does the radio work OK, and have you checked all the tubes in a tube tester? I ran a Comstat 25 for many years back in the '60s and it was a great rig. My only complaint was that the crystals kept messing up and the channels would go out, since it was a frequency synthesized radio.

[dime196604]

the radio turns on but it has no transmit and the receive cuts in and out

[TheSpaceMan]

the radio turns on but it has no transmit and the receive cuts in and out

That radio is around 45 years old, so definitely some tubes could be NG! I'd first check all the tubes in a tester, and replace any that might be bad. See if you can find a local ham operator who could also check out the circuits for you. Do a search for a website called eHam where you should find some local hams in your area who are familiar with old tube type radio equipment. You may run into some HAMS who dislike CBers, but there usually are a few who would not mind lending you a hand.

[A NUMBER 1]

You stated the radio turns on but No transmit,if it has the original mic ,the wires on the mic may have become brittle and even need to be redone,I have noticed this t obe pretty common when over a long period of time the mic s have not been used or are real old...A NUMBER 1

[dime196604]

You stated the radio turns on but No transmit,if it has the original mic ,the wires on the mic may have become brittle and even need to be redone,I have noticed this t obe pretty common when over a long period of time the mic s have not been used or are real old...A NUMBER 1

it came with a D104 wire to it all ready. Like i said the RX cuts in and out. And it has no TX but i can here something clicking inside the radio when i key the mic, that give you any ideas?

[Night Crawler]

i can here something clicking inside the radio when i key the mic, that give you any ideas?

That's the relay so it's switching between receive and transmit.

[TheSpaceMan]

i can here something clicking inside the radio when i key the mic, that give you any ideas?

That's the relay so it's switching between receive and transmit.

Yep, that's the relay. Now the next thing to check is whether any carrier at all is being generated on any channel. He will have to key up on each channel and check with a nearby radio or field strength meter. Sometimes a bad crystal (or crystals) can prevent the unit from transmitting. It is also possible that he may have a carrier but no audio. If I remember right, my Comstat had a 100 milliwatt/5 watt switch on the back! If he has the same unit, make sure it is switched to 5 watts.

[Night Crawler]

If I remember right, my Comstat had a 100 milliwatt/5 watt switch on the back! If he has the same unit, make sure it is switched to 5 watts.

The Comstat 25 in that series was the only one that had the 100mw switch the A&B didn't.

[dime196604]

I had it hooked up to a multi meter and it didn't throw any power out at all and would even make any of the needles twitch at all and could not calibrate for modulation.. I think i might take her to the shop when taxes come.. hope i can afford it

[TheSpaceMan]

I had it hooked up to a multi meter and it didn't throw any power out at all and would even make any of the needles twitch at all and could not calibrate for modulation.. I think i might take her to the shop when taxes come.. hope i can afford it

LOL! See if you can find a friendly local older ham in the area who is familiar with tube equipment. Some of those guys love to tinker with old radios, so you might even get it patched for free!

[Night Crawler]

I had it hooked up to a multi meter and it didn't throw any power out at all and would even make any of the needles twitch at all and could not calibrate for modulation.

I wouldn't expect it to that's not what a multimeter is used for just curious what was it hooked to on the radio?

[dime196604]

I had it hooked up to a multi meter and it didn't throw any power out at all and would even make any of the needles twitch at all and could not calibrate for modulation.

I wouldn't expect it to that's not what a multimeter is used for just curious what was it hooked to on the radio?

Sorry when i said multi meter i was referring to my 3 way cb tester. you know the one with SWR/power/modulation.

[dime196604]

Gonna take this radio to the local tech... He says he still has a lot of lafayette tubes left from the 70's back when they were popular.. It will be sweet because then it will still be bone stock and all the tubes will still say lafayette on them... Can't wait

[The Shadow]

Make sure that tube with the blue glow gets replaced because it's bad. Blue glow in a tube is caused by gas that shouldn't be there. Make sure your tech replaces not only the electrolytic filter caps but ALL paper/wax caps too. If they're not bad now they WILL go bad later and can take out an expensive part when it does.

Terry

[dime196604]

Make sure that tube with the blue glow gets replaced because it's bad. Blue glow in a tube is caused by gas that shouldn't be there. Make sure your tech replaces not only the electrolytic filter caps but ALL paper/wax caps too. If they're not bad now they WILL go bad later and can take out an expensive part when it does.

Terry

That seems like it would cost way more money then it would be worth....

[Nagant]

Make sure that tube with the blue glow gets replaced because it's bad. Blue glow in a tube is caused by gas that shouldn't be there. Terry

Gassy tubes have a blue glow but it's more intense with other colors and tends to change in intensity as well. Such as:




He had mentioned in another post about the blue glow he was seeing and it seemed he explained it as more of a haze that didn't change in intensity. A long time audiophile who holds some electronics engineering degrees informed me that type of blue glow/haze has to do with stray electrons interacting with impurities in the glass and therefore it's nothing to be concerned with. That type you see more in the glass and not in the envelope. I tend to believe him as I have seen this phenomenon many times in tubes that test fine on a mutual conductance tester and perform without issues in circuit. Therefore the reason I brought this up as I believe there are two different blue glow phenomena that happen with electron tubes that aren't related.

[The Shadow]

[/quote]
That seems like it would cost way more money then it would be worth....[/quote]

Not really. Depends on how much your tech charges for labor. The caps themselves average around a buck a piece depending on the value. I just finished re-capping a Robyn T123B which is the same chassis as a Lafayette Comstat 25A. Including the filter caps there's only about 10 caps that need replacing. Most of the caps in these sets are ceramic disc which hardly ever go bad. Shouldn't take your tech more than about a half hour to replace them. It's a lot cheaper than replacing a burned out power transformer later. If you know how to solder you can do it yourself. Capacitors and resistors are the most common components that go bad in tube radios. Much more so than the tubes. These parts were never designed to last for 50 years.

Terry

[dime196604]

Make sure that tube with the blue glow gets replaced because it's bad. Blue glow in a tube is caused by gas that shouldn't be there. Terry

Gassy tubes have a blue glow but it's more intense with other colors and tends to change in intensity as well. Such as:




He had mentioned in another post about the blue glow he was seeing and it seemed he explained it as more of a haze that didn't change in intensity. A long time audiophile who holds some electronics engineering degrees informed me that type of blue glow/haze has to do with stray electrons interacting with impurities in the glass and therefore it's nothing to be concerned with. That type you see more in the glass and not in the envelope. I tend to believe him as I have seen this phenomenon many times in tubes that test fine on a mutual conductance tester and perform without issues in circuit. Therefore the reason I brought this up as I believe there are two different blue glow phenomena that happen with electron tubes that aren't related.

The glow is just a light blue haze it is no where as intense as the one in the video.. but that tube with the glow gets hotter then hell after a few minutes.. but like i said its going to the Dr in a week or so.

[dime196604]

Ha Ha, spent a week pulling all the tubes and cleaning the sockets, cleaned the crap out of the relay with some electrical contact cleaner, cleaned all dirt and grime from chassis that every thing sits on, turned it over and cleaned the dust and greasy crap off the electronic side with all the capacitors. Got it as clean as i could for its age. Well all in all, now the radio power up and transmits!!!! does around 10 watts, the receive still cuts in and out a bit, but it seems to be getting better the more the dial gets turned, This leads up to my next question, what is a good way to clean the channel selector? not the out side part but the part inside the radio, the part that links all the crystals together, i would use the contact cleaner on it but there is some type of lubricant on it and i did not wanna strip it off with the contact cleaner. Rat shack sell this stuff for cleaning potentiometers it says it cleans the pot and lubricates them at the same time, would this be a good thing to use to clean this?

[The Shadow]

Spray the cleaner on a Q-tip and use that to clean each contact on the switch. Dirty contacts is probably the reason for the intermittent receive. An old toothbrush is even better if you can get it in there. Then turn the channel selector through it's complete range, back and forth a couple of times and you should hear an improvement. You also might want to remove the crystals, one at a time, and use some fine sandpaper to clean those pins.

Terry

[Nagant]

Don't spray any lubricants in it. That's asking for big troubles. The Shadow gave you some good advice. Contact cleaner sometimes works but Deoxit would be a better choice.

[dime196604]

Don't spray any lubricants in it. That's asking for big troubles. The Shadow gave you some good advice. Contact cleaner sometimes works but Deoxit would be a better choice.

What is Deoxit? were can you find it? I did like the shadow said, now i almost got every channel, channels 3, 8, 18, and 23 still come in and out. mostly out, but its a 100 times better then it was before, a little more cleaning and we should be good to go. After i get all the channels working it will be time to replace all the capacitors underneath, then i will have a nice 23ch tube radio..... Is it possible to convert it to 40ch?

[Nagant]

Google Deoxit.

I'd try a few more applications of cleaning as you have already since it improved it before buying the Deoxit.

[The Shadow]

Here's where I usually get my Deoxit:
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Look under Tech Supplies and then Chemicals and then Cleaners.

It's possible to convert a crystal set to 40 channels but I wouldn't recommend it. It's complicated, requires a bunch more crystals (good ones getting harder to find and more expensive) and other parts. Back in the day, they used to sell conversion kits. I have a Robyn T123B I'm working on now that has one of the kits installed. It's a major PITA. A lot of the extra crystals are dead or off frequency. It's also a challenge to figure out. It involves a second bank of tx/rx crystals, a second mixing crystal and a 2 position toggle switch plus a 12 position rotary switch to mix it all together!

Terry