Dynascan Cobra Cam 88

[Rumrunner]

This old rig was my first experience at a real base radio. Like a lot of others, I want to re-create my old school stations.. .Now I remember there was a "tweek" for the Cam 88 (maybe modulation section tube change?) Anyone remember the "mods" for the Cam 88? Thx and '73 from the (very wet) swamp. - Rumrunner

[Sandbagger]

Jul 7, 2013 4:12:15 GMT -5 Rumrunner said:

This old rig was my first experience at a real base radio. Like a lot of others, I want to re-create my old school stations.. .Now I remember there was a "tweek" for the Cam 88 (maybe modulation section tube change?) Anyone remember the "mods" for the Cam 88? Thx and '73 from the (very wet) swamp. - Rumrunner

Recreating your old school setup is a lot of nostalgic fun. I still have my original Lafayette Comstat 25, and it's needed a bit of TLC to keep going.

There were a bunch of "tricks" back then that people tried to squeeze every little bit of power out of these radios. The most common mod was to jump out the plate voltage dropping resistor for the final tube. This was usually good for jumping the power up 2 or 3 watts. The problem was that it lowered the modulation somewhat in exchange for that larger dead key. When I rebuilt my Comstat the first time, I noticed that this mod had been done to mine, and I removed it. The power dropped from 6 watts carrier to 3 watts. But the modulation got much cleaner and had more punch.

There are some other, more extensive, mods which involve tube changes and what not. These are not something to attempt for those who are not familiar with tube circuits and their particular issues. Some have claimed upwards of 20+ watts out. But I don't know how this effects the modulation or what additional stresses this puts on the power supply.

So I would stay away from power increasing mods and just let the radio run as it should. If you need more power, just get an amp and let it do the work. Find a nice D&A Raider or a Wawassee Black Cat, and it'll be all vintage gear.

[2600]

I'm gonna chime in with Sandbagger here and echo his advice.

A chain is only as strong as its weakest link. The engineering inside that radio did not include any "extra" power that you can effectively tap into. The power supply, audio amplifier and RF final stages are exquisitely matched to such a degree you can only get a "cosmetic" improvement with any of the mods I remember.

Pull harder on the chain and that weakest link is always the one that breaks.

Of course, you can always put a nitrous bottle on the tiny 4-banger in your wife's daily driver. But it won't last as long that way. And a radio is not a car. Crossing the finish line 1/10 of a second before the other guy makes you a big winner on the track. To see just one-half of an S-unit improvement you need to double your wattage.

The added wattage you can get is not enough to show up on the S-meter at the other end. That's what matters, after all. Another 20 percent on your wattmeter may look like a lot. But it's not enough of a boost to move that S-meter needle upwards by even the thickness of the pointer.

This is not to say that some audio "tweaks" can't get you a better sound. More audio power will make you louder, even if the wattmeter reading didn't improve by much.

But I'm not a Cam-88 expert. Trust your ears. If you think a mod makes it sound better, go for it. Most any mod that boosts the carrier power will reduce your modulation level, like the man said, unless you also find a way to get more audio power from the audio tube at the same time.

73

[Rumrunner]

Thanks for the reply's, Guys.

Since you don't know any of my background I'll give you a little. I was raised in a radio/tv repair shop in the early sixties thru the seventies.

I restore all my own gear. Currently working on a Swan line-up (250, 500, 700 ss-16, Siltronics 1011-d). I've repaired tube amps since before I had a drivers license.

I found the information on enhancing the audio on my Johnson blackface (I had already reversed the high-power mod on it) and would like to find more info on the Cam-88 for audio mods etc.. If it has any power mods they will be reversed.

Once the radio has the sound I want I can "raise the s-meter" on the other end I think - I just need to get some cooling fan noise issues addressed.

I want to thank you both for trying to keep me from whacking a nice old rig. What I found out way back was the mod section in a lot of the old bottle rigs was good for legal output and not much more. I seem to remember a modulation tube upgrade for the '88 and that was what I was hoping to find.

'73 from the swamp!

[Sandbagger]

Jul 7, 2013 23:31:21 GMT -5 Rumrunner said:

Thanks for the reply's, Guys.

Since you don't know any of my background I'll give you a little. I was raised in a radio/tv repair shop in the early sixties thru the seventies.

I restore all my own gear. Currently working on a Swan line-up (250, 500, 700 ss-16, Siltronics 1011-d). I've repaired tube amps since before I had a drivers license.

I found the information on enhancing the audio on my Johnson blackface (I had already reversed the high-power mod on it) and would like to find more info on the Cam-88 for audio mods etc.. If it has any power mods they will be reversed.

Once the radio has the sound I want I can "raise the s-meter" on the other end I think - I just need to get some cooling fan noise issues addressed.

I want to thank you both for trying to keep me from whacking a nice old rig. What I found out way back was the mod section in a lot of the old bottle rigs was good for legal output and not much more. I seem to remember a modulation tube upgrade for the '88 and that was what I was hoping to find.

'73 from the swamp!

Ok, well that's a horse of a different color. If audio mods are what you are seeking, you can't really go wrong if you know what you are doing. Usually changing the values of coupling caps can bring up the low frequency end for a more pleasing sound.

You're right in that the audio output in those tube rigs (and most solid state radios as well) is just enough to fully modulate a stock 3 - 4 watt carrier, and some fall short even at that level.

There are things you could probably do to boost audio performance, by changing output tubes etc. Assuming you have enough power in the supply to handle it. There were probably detailed generic mods which could be adapted to work for specific rigs. There really wasn't all that much difference under the hood between most of the old AM tube rigs of the 60's, so what worked on one could be made to work on another. The problem is that back in the day, when the true tube radio pioneers were engineering these mods, they were basically hand written drawings which tended to stay local to that particular engineer. There was no internet (or even a photocopier) to share those great innovations back then. That's why you'll find hundreds of mods on the latest radios but next to nothing on the old stuff.
Just digging through my old files, and I've come across some amp bias tricks, a few "birdie" schematics, frequency mods, and a power tube mod for a Hy-Gain 623. But nothing for high fidelity audio. You may have to do your own engineering on this one. A good place to start is the audio section of a Tram D201. It used a 6L6 audio power tube, which should be enough power for any thing you'd want to do. You may be able to adapt elements from that, although the 6L6 may not fit inside the case of a CAM 88

[BBB]

I have a Cam 88 and the similar Cam 98. Sandbagger did a nice review of the Cam 98. home.ptd.net/~n3cvj/cam98review.htm

Great looking radios. Another version was the Allied 2567.

I read that people used a B&K (Cobra) CA-300 Compressor device with them to improve the audio. I started looking for one and found a few adds, but they were already sold.

Old sale description by others found :

B&K Model CA-300 Compressor-Amplifier -
transistorized.
Neat little package great for processing AM speech
envelope for greater talk power.
I think this may also be a limiter.
Has two adjustment controls on the front panel for
compression, level, and on-off switch.
Neat little green cabinet with rubber feet.
Input jack uses a large 4-pin female connector and
the output is via a shielded cable with a male 4-pin connector.
Uses 9V Battery.

[spitfire441]

Jul 8, 2013 10:15:33 GMT -5 BBB said:

I have a Cam 88 and the similar Cam 98. Sandbagger did a nice review of the Cam 98. home.ptd.net/~n3cvj/cam98review.htm

THE BUS!

[BBB]

[Sandbagger]

Jul 8, 2013 16:47:00 GMT -5 BBB said:

More like:

home.ptd.net/~n3cvj/bluebird_cobra.htm