PAL 351 BDX LINEAR

[tulmkr]

Hi FOLKS, Ive picked up this little amp, and its started to grow on me. I know the tubes are a bit pricey, so a full swap wont happen right away. The amp is deadkeying 250 on high, and swings to about 375-400 when good and warm. Thats about the limit for this amp, but I noticed the driver tube tip is loose. Does this affect the performance of the tube? Perhaps a fresh driver tube would put a little life back into it?

Any help or advice is appreciated. I bought it to use as a driver for a heathkit sb200.

[crazy_cooter]

It's pretty common for tube caps to loosen up. As long as it doesnt break off you should be ok. I'm not real sure but someone told me it causes grid leakage in the tube, but i dont think it affects anything. I have loose tube caps on some of mine and they work ok. Just be very careful not to twist on it, then you'll be buying a tube.

[231]

I had a PAL 321 for awhile, it was a decent little amp with 1 driving 3 x 8950's. Great audio out the amp though. I'd say if it's anything like the 321 I had you are seeing about average for what it should do.

On another note I'm sure you are already aware of it, but the SB-200 can only take 100w of drive, and the 2ea 572b's are only good for 600w or so max (usually closer to 500w on 10m). Most of the guys I know running the SB-200 nominally run them at about 400-500w anyway so they last. I could be wrong but I think the only one going to see a signal difference between the two amps is you and your meter. Over drive the SB-200 and you are likely to start seeing some problems with it I'd guess. I've had one of those too and it was a good little amp. But it certainly isn't going to like being driven too hard.

Best of luck and welcome to the forum.

[crazy_cooter]

I have a Pal 351 for parts...no tubes in it though. It's the silver faced one thats flat, and the tubes mount horizontally right? It's buried in my shed with a bunch more dead equipment

[Ohio_359]

but the SB-200 can only take 100w of drive,

This is correct, and 600 out is good. It's a kilowatt amp, meaning a kilowatt "input" at 60% efficiency gives you 600 watts out.

Also, I'd personally be leery of a tube with a loose plate cap, the getter is only capable of so much "getting".

[Nagant]

That carrier output from the amp is a bit on the high side. I would turn down he carrier from the radio so the amp will have a carrier output around 90 to 125 watts or so. No need stressing those expensive and hard to find sweep tubes that amp uses. Loose plate caps can be resecured with some epoxy. I just dab some around the bottom edge of the cap with a plastic diddle stick. If they are really loose you can get it up under the edge of the cap if you're real careful. If it's not that loose then just allow some over on the glass as well. Might not look pretty but it has always worked for me.

I completely agree with 231. Your PAL is to much drive for an SB200.

[crazy_cooter]

That carrier output from the amp is a bit on the high side. I would turn down he carrier from the radio so the amp will have a carrier output around 90 to 125 watts or so. No need stressing those expensive and hard to find sweep tubes that amp uses. Loose plate caps can be resecured with some epoxy. I just dab some around the bottom edge of the cap with a plastic diddle stick. If they are really loose you can get it up under the edge of the cap if you're real careful. If it's not that loose then just allow some over on the glass as well. Might not look pretty but it has always worked for me.

I completely agree with 231. Your PAL is to much drive for an SB200.

[Night Crawler]

That carrier output from the amp is a bit on the high side. I would turn down he carrier from the radio so the amp will have a carrier output around 90 to 125 watts or so.

That's what the carrier output should be if using it on AM follow the ratings used for SSTV (slow scan television) and it will work fine.

Run the SB200 at a 600 watt carrier output on AM and watch the plates of the tubes slowly turn from a deep red then to orange until there's a fireworks display in the envelope of the tubes.

[Ohio_359]

Run the SB200 at a 600 watt carrier output on AM

Huh? You can't even run it's big brother that hard.

[Night Crawler]

Run the SB200 at a 600 watt carrier output on AM and watch the plates of the tubes slowly turn from a deep red then to orange until there's a fireworks display in the envelope of the tubes.

Run the SB200 at a 600 watt carrier output on AM

Huh? You can't even run it's big brother that hard.

Next time when you quote me don't edit it and read the whole post!

I was advising not to run the SB200 at a 600 watt carrier level on AM I built and used one of those amps for many years and if used for AM linear amplification the carrier output should only be at around 100 watts to keep the tubes within their ratings.
If run harder the plates of the tubes will not be able to dissipate the wattage lost in heat which will cause them to turn red then orange and eventually fail.

[Ohio_359]

Next time when you quote me don't edit it and read the whole post!

Who suggested trying to get a 600 watt carrier out of a set of 572b's? I guess that's the part I missed.

BTW, I didn't edit anything.

[Nagant]

Um yes you did edit the quote as you didn't include Night Crawler's entire sentence and therefore it was presented out of context which resulted in a different meaning.


Big difference between:

Run the SB200 at a 600 watt carrier output on AM

and:

Run the SB200 at a 600 watt carrier output on AM and watch the plates of the tubes slowly turn from a deep red then to orange until there's a fireworks display in the envelope of the tubes.

[Ohio_359]

A "partial quote" and an "edit" are 2 different things. Yes I partially quoted, no I didn't edit.

But my point is, I don't see where a 600w carrier was suggested.