Sweep tube suggestions

[rsumperl]

Greetings everyone,
I could use some suggestions on designing an amplifier with sweep tubes. I am looking for power in the 85-115 watt range. I have 750v @ 350ma and a regulated 250v @ 150ma available. I'm thinking of class AB1, or AB2 maybe even class B operation. This amplifier will be a modulator for an AM transmitter.

Thanks,
Ray

[KE6DF]

I think a good choice would be a pair of 6DQ5's or perhaps two pair of them would be even better.

Two pair of 6BG6's (basically similar to 807s) would also work.

The above are cheap and easy to come by.

Others like 6LQ6s and 6KD6s would also work, but they are expensive.

You can also use the higher voltage tubes like 36KD6s to save a little money -- but they are still more than 6DQ5s

[N2DTS]

Why use sweep tubes?
They were for TV sets, if I want an audio amplifier, I would tend to use audio amplifier tubes, not TV sweep tubes.
You can get KT88's or KT90 hifi tubes and get lots of low distortion power out in AB1....

The G76 used two 6dq6 tubes to modulate a 6dq5 (or was it the other way round?), using the screens as the grids in zero bias, try finding any spec's for that setup!

Brett

[WBear2GCR]

Why use sweep tubes?
They were for TV sets, if I want an audio amplifier, I would tend to use audio amplifier tubes, not TV sweep tubes.
You can get KT88's or KT90 hifi tubes and get lots of low distortion power out in AB1....

The G76 used two 6dq6 tubes to modulate a 6dq5 (or was it the other way round?), using the screens as the grids in zero bias, try finding any spec's for that setup!

Brett

Sorry, I'm going to disagree here.

Pairs of Kt88s are good for ~60-75 wrms out.
Pairs of KT90s are good for a bit more but not that much more.

Quads of tubes will get you into the >100 watt out range. (Using "normal" plate voltages for audio tubes.)
Harder to find iron with the requisite windings on the primary...

You can get a solid 200w out of 4 x 807 in AB2 at around ~750vdc B+.

Sweep tubes can be "pushed" substantially beyond their rated B+ in intermittant service, so one could maybe get that much out of a pair. They also will stand more current in intermittant service. I certainly get ~150% positive modulation  (maybe more) using a pair of some darn sweeptube (drawing a blank at the moment) in the modulator of a Valiant II. The better sweep tubes can likely handle >100w out in this service... regular audio tubes, not.

But I'd go for a pair of 811As for a modulator in this class. Simpler and easier assuming you have iron to match, plus you get headroom - depending on B+ available, 175wrms is possible. AB2 is my preferred mode of driving output tubes.

Just my opinion...

[N2DTS]

No.
I run KT88's in the 32V3, at 700 volts I get way more than enough audio to modulate the rig.
A pair of KT88's are good for 100 watts out in AB1 at 550 volts, 2.5% distortion....

The KT90, at 750 volts on the plates, 600 volts on the screens will do 160 watts out.

There are lots of better tubes for modulators then sweep tubes, even 809's or 811's would seem better then using sweep tubes....

Even four 1625's or 807's will get 240 watts or more, and you can likely get them very cheap.
(I just gave a bunch away)


Brett

[KC4VWU]

It also really depends on how complete you are on the parts list. You appearantly have a supply. If you still have to get mod iron, tubes, etc.; I'd go with 1625's for that power level. They're still pretty cheap and easily obtainable; although at the prices they can be had for now, I'd buy up a small stock of them. I know there are several handbooks with the calculations already worked out and construction details. Build it up as shown, then go back in and do some step by step optimizing to suit your needs.

I'm contemplating a pair or quad of 4-65A's modded by either 811A's or 813's. But then, I'm pretty much set on go for the parts. All I need to do now is a little calculating. It will be my first attempt at a decent sized HB tx.

Phil

[N4LTA]

I just picked up four 4-65s and have a couple of sockets. I am thinking about two 4-65s modulated by a pair of 811As. If you decide to go with the 4-56s , I'd like to see what you are planning.

Pat
N4LTA

[KC4VWU]

O.K. Pat, I'll work on a schematic and start a new thread when I get it finished. I'm definately gonna need some proofreading on it. Just at a quick glance, 1500v should be good for an easy 200w carrier for a pair.

Phil

[w4bfs]

if you are considering a 4-65 modulated final, I would talk to Sam KF4TXQ about them .... biggest problem is high impedance

[KE6DF]

Back on the original subject -- sweep tubes for modulators.

While the 1625 or 807 are good transmitting tubes,

I would think that a pair of big sweep tubes would put out more power in class ab1 or ab2.

They are also designed for high voltage and current peaks and have more filament emission than 1625s.

Those are good things in a modulator, it seems to me.

The largest one around, I think, is the 6lw6 -- although they are a bit pricey.

[N2DTS]

All that might be true, although the high voltage limit on most tubes is way lower then it needs to be, I run 4D32's at 1200 volts, TWICE the recomended voltage without problems.

With sweep tubes, whats the operating points?
What is the distortion?
Where do you set the bias for lowest distortion?
If class B, what is the drive and grid voltage swing needs?


You wont find much/any info about all that, but will find tv sweep info...

Brett

[KE6DF]

Here is data on AB1 operation of a few sweep tubes, compared to various other tubes, and including distortion.

Note how the 6DQ5 shines relative to the 807 in both power output and IMD.

The link says the data came from an Orr handbook.

Dave

http://jlandrigan.com/files/6dq5_and_other_tube_specs.pdf

[N2DTS]

That info says the sweep tubes are worse, with imd, a higher number is better, that is, -30 is better then -28.
The 6dq5 is the same as the 807 at the same plate voltage.
And notice how much better the hifi 6550 is!

I bet the KT88 or KT90 would be even better....

Brett

[WBear2GCR]

Brett, I may be wrong, but for now we'll have to disagree?

Afaik KT88 = 6550 for all intents and purposes.
If you talk to Nick KG2IR I am confident he will tell you that a KT88 will not equal a 6550.

The KT90 is a new tube, and you may be right about its capabilities... I dunno.

As far as running tubes above their "book" ratings, that can be done with some and not with others.
The 807 and 4D32 are two that will fly that way.

I've never seen a quad of 807 in AB2 do 240 watts, 200 yes. Maybe you could push them with higher still B+ and get to 240w. Dunno.

Anyhow the question was which sweep tubes to run in a modulator... I say run whatch brung!

                      _-_-bear

[KM1H]

There is certainly nothing wrong with sweep tubes for modulators especially if run a bit below their maximum ratings. Sylvania published parameters for SSB service back in the 60's as well as Orr which will give you bias and idle current data.

I like 6BG6's and 6DQ5's, they are not as powerful as the color TV versions such as the very pricey 6LQ6 family but they are almost free and if 2 dont give enough power then use 4 in PP parallel.

The 4D32 is another nice tube and a pair will run well over 200W at a sane 750V.

Carl
KM1H

[KE6DF]

Well, going back and looking at the numbers, the 6DQ5 -26 db on the 3rd order IMD column (far right in the table) and the 807 is -23 db. But you are right, at higher voltages like 700 they are nearly equal.

So maybe "shines" was an overstatement on my part.

It's also interesting that the 6LQ6 has the highest distortion in the table.

And that tube was one of the ones used in the "crappy" "10 meter" linears that were sold to CBers back in the '70s.  

On top of that, the tubes in those days were pushed past their limits and those linears had a reputation for eating tubes along with crappy signals.

I'm surprised more people don't use the 6550 in low and medium power ham radio applications.

You are right those really stand out. But they are usually expensive

Not worth debating all day, but it sure looks to me like the 6DQ5 anyway is a good modulator tube -- and it's one of the cheapest sweep tubes.

I too consider the 4D32 one of the best tubes going.

Dave

[KD6VXI]

On top of that, the tubes in those days were pushed past their limits and those linears had a reputation for eating tubes along with crappy signals.

The biggest problem with that was that the CBers typically took the number on the front (Model) to mean the dead-key power of an AM signal...

They lasted forEVER when run sanely.... I have a WELL used Pal 201BDX (pair of 8950s) I just rebuilt (removed driver tube, installed tuned input), original pal tubes in it.  It will still make > 350 watts, but run at 200 PEP, it has lasted 30+ years.

NOT to mention, IMD goes WAY down when the sweep tubes where run at 100 watts PEP...  Most CBers ran them at 200-275 PEP each.

--Shane

[N2DTS]

You wont find hifi tubes in RF service because they had no plate caps.
You won't find hifi tubes as modulators because they were more expensive then something like an 807 or 6146.

The makers of 'ham gear' did nothing to improve the audio quality, and would not spend a dime more then they had to to get a working rig.

Brett

[W1RKW]

Then there was the 6MJ6 which was a beefier version of the 6LQ6. Probably the beefiest of all the sweepers.  There were some amateur sweep tube amps as well that used the 6LQ6 and some the 6MJ6.  I think the AL-84 by Ameritron used 4 6MJ6's.

found this on the 6MJ6.  http://www.thermionic.org/sw6mj6.jpg

These are expensive if found.

[Opcom]

The 6CD6 is a tough tube, takes up to 1000V on the plate, and needs only 200V on the screen. It drives like a 6L6 and cost about $6. I used a pair for audio and they worked quite well. Lots of current available from its cathode too.

[KD6VXI]

The 6CD6 is a tough tube, takes up to 1000V on the plate, and needs only 200V on the screen. It drives like a 6L6 and cost about $6. I used a pair for audio and they worked quite well. Lots of current available from its cathode too.

The 6LX6 will take 1150 volts on the anode, and surprisingly, for quite some time!

They used it as a driver on the JB2000.  It will make 175-200 PEP.

--Shane

[KD6VXI]

Then there was the 6MJ6 which was a beefier version of the 6LQ6. Probably the beefiest of all the sweepers.  There were some amateur sweep tube amps as well that used the 6LQ6 and some the 6MJ6.  I think the AL-84 by Ameritron used 4 6MJ6's.

found this on the 6MJ6.  http://www.thermionic.org/sw6mj6.jpg

These are expensive if found.

The 'BEST' 6MJ6 you can get is the "RF Black Cap Double Strapped Plate" version, I believe, by sullyvania. (I could be wrong on the mfg, it's been 20 years).  It has different Cout and Cin than the standard 6MJ, but had a double strap to both the anode (which provided more cooling and less L to the anode) and the cathode (less L).  It was a GREAT tube for RF service, but was a sweep tube.....  By the mid 80s, there was the telltale signs that they where going byebye (and had been for a decade).

The 6MH5 is also another BIG tube, as far as sweepers go.  It's a plug in for the LF6, and has about 20 percent more Pdiss.

--Shane

[W1RKW]

Shane,
I think the plate cap on the 6MJ6 was actually an integral part of the envelope unlike other sweep tubes where the cap was glued on and soldered or crimped to a thin wire coming through the envelope.  The 6MJ6 also had thicker glass if I remember correctly.

[KM1H]

You wont find hifi tubes in RF service because they had no plate caps.

Tell that to anyone who ran a CE100V or 200V; I had both along with a pair of 75A4's in my early contest days. 100W out even on 10M from 6550's and very rugged. I still have a few sets of NOS matched 1960's TungSol.

Carl
KM1H

[N2DTS]

I would think it would be hard to keep the plate and grid stuff apart, or not have the tube socket arc with all the plate voltage on it.

I can see why they would want to use them though, since they were low distortion.

Brett