Question for the Tube Guys..... 752B`s

[AudioShockwav]

The Ameritron 811 Amp, 3 811`s all band, small and not to expensive, well at least to most of the bigger amps.
They can be found used for a good price of you look around. 811`s are cheap.
Works decent, not the best, but it is still a good starter amp for someone that needs all band coverage to work HF.

We all know that you can drop 572`bs in the holes and they work just fine, not really any improvment in gain, due to the fact that the HV section (powersupply) is not up to job of feeding 572`s.
Ok here is the question.
What can be done to improve the peformance of this amp, running 572b`s?
What areas of the amp need to be looked at in terms of supplying correct filament voltage, how much is the power supply capeable of....can fairly small changes be made in parts ratings/values that would improve this amp using these tubes.

In some cases, I would just say, sell it and buy a bigger amp....but the idea here, is if you have one(a 811a) and a shack full of "Junk" (read spare parts all over the place) and some time to play radio, what are some ideas......
Anybody up with any ideas?

73
Jeff

 

[W5LZ]

Jeff,
What you might do is contact the repair department of Ameritron. Ask them the same questions. At one time it was fairly common practice for them to tell you how to do that modification. That was some time ago, so things can certainly have changed now. It isn't impossible at all, just not super simple as swapping tubes (like you didn't know that ). Just swapping tubes has a down side. You actually loose a little output power. The positive side of that is that the @#$ thing will last forever, you can't make an amplifier any more 'solid' than that.
One of the 'tricks' for dropping the filament voltage was to use 'ni-chrome' wire for the supply to the filament pins. The length of that wire determines the voltage dropped. Way too long since I've even thought about that so no idea as to lengths. The plate voltage 'boost' was simple, use one of the lower taps for the buck/boost. If you really wanna get 'picky', start changing the caps to a larger voltage rating. Then there's the 'little' things, recalibrating the meters for voltage supply increases and changing the light bulbs (nice time to swap them over to LEDs!).
Went though the 811/572 thingy more years ago than I want to remember. Had the 572s, didn't have the 811s. Found the 811a, saved the 572s for emergencies, sort of, just to lazy to do the 'rest' of the mods (and fell in love with the 3-500s!). Want an 'AL-811' serial number 13? I'll make you a totally ridiculous deal on it... send blank check. Then hold your breath, like I am waiting on that check.
- 'Doc

 

[lords]

lol,Doc now thats a trip..lol

Checks in the mail....
the thing is ,is it well worth it?
but i do see some taking a heathkit200 and converting it to the 3-500's
I love the glow on them tubes
now taking a SB220 and putting converting it to 2 3-1000 is next
seeing though it can handle it as the transformer is underrated
and yes I do know theres more involved in this converting

as for them Ameritrons well I think they make them underrated too if i am right?

 

[W5LZ]

I think I may have given the wrong impression about that 'AL-811' and 3-500s. No, you can't go that way with a tube swap, not without completely stripping and rebuilding the thing. About the only thing that could be reused in/as a 3-500 tubed amplifier is the cabinet and RF section, sort of. Just not worth the trouble, all things considered.
Same, if not more-so with the SB-200! The least of which problem is that a 3-500 can only be laid down in one of two positions and be expected to 'live' for more than a few mili-seconds, once voltage gets to the plate. Same for the 572s. Better pay attention to the positioning of the tube socket(s) - lol!
The 3-500 thingy is sort of a complicated story. Had one friend who wanted an 'AL-600' when they first came out, couldn't get on the waiting list. Had another friend who happened to get on the waiting list -twice-! Got both 'AL-600's (you believe that?). Had a 'brain-storm' and said I'd take the second one off his hands, if he wanted. Oh the gratefulness over flowed! Then told that 'first' friend that I just happened to have a new 'AL-600' and didn't know what to do with it cuz I'd really wanted an 'AL-80'... (which he just happened to have as a diver for his home-brew amplifier). Three hours later everybody was happy! Besides, I wanted to see that amplifier that used an 'AL-80' as a driver. Did see it. All I'll say is that you could drop a piece of 'texas-toast' through it's tuning capacitor's plates without ever getting crumbs on them. I couldn't afford to turn it on, much less pay the electric bill. That was a good 20 years ago, still have the 'AL-80A', added a 'B' model just because it was lonely and am amplifier poor.
You can send that blank check if you want to, but don't ever expect to see the 'AL-811'! It really isn't for sale (@#$ thing still works).
- 'Doc

Now, it's field day, I'm supposed to put up antennas, I'm out'a here.

 

[AudioShockwav]

!). Want an 'AL-811' serial number 13

# 13?
How long have you had that thing Doc?


73
Jeff

 

[W5LZ]

Jeff,
Had it since it was brand new, literally. Can't remember when I bought it, just after they started advertising them. If I had it to do over again, I think I'd have been smarter to have waited a few months longer. It's been back to 'Ameritron' twice. First was a general factory fault they found with the original models, no cost at all sort of fix so you know it was their fault - lol. Second time was my fault, and I didn't have the time (or the nerve) to fix it my self (no warranty, all my cost).
After a few other amplifiers in the mean time, I've got another 'Ameritron', not new, but nothing wrong with it either, that I can't fix (burned out meter light).
I've come to the realization that if you wait just a little while, let all the 'bug' get worked out of the 'latest and greatest' new thingy, then buy it, you come out ahead in the long run.
Long answer to a short question, huh?
- 'Doc

And I really hate to say it cuz I have a reputation for 'cheap' to uphold, but the AL-811 isn't for sale. ... Unle$$! ... Naw, nobody's that stupid.

 

[W5LZ]

Lords,
Just noticed the part about the transformer in an SB-220 being 'underrated'. OOOooo is that statement wrong. If anything, it's overrated! Easiest 'upgrade' for more power out of an SB-220 is to dump the stock trnasformer and installing a 'Peter Dahl'. Certainly not the cheapest, but probably the simplest. 'Peter Dahl' has two transformers for the SB-220. One will fit in the original case, takes some squeezing, but it'll fit. The second transformer requires external mounting. The second can, and will, make an SB-220 into something else altogether. An SB-220's typical "input power ratings" then turn into a 'tad' bit less than what that larger transformer conversion's typical results are. A much larger cooling system is also required. The stock transformer can't get close no matter what you change the tubes to.
- 'Doc

You wouldn't need a filament transformer for an SB-220? Think I have one around here somewhere, maybe. All that's left of that @#$ thing, thank goodness!