Using sweep tubes for modulators

[kb3ouk]

I think I got some 6CD6s in my tube stash out in the shed. Might try building a pair of those modulating a 1625 (got one of them out there too, that's why) or use another pair of 6CD6s in the final as well. Wonder how well that would work?

I've never seen one in RF service, only in class C as TV horizontal sweep amplifiers (fundamental about 100Khz) and in medium voltage power supplies as pass regulators. 160M and 80M sure, but at some point there may be issues. Compare the interelectrode capacitances to RF tubes like the 6146 and also look at one visually to best consider the internal inductance of the connections to cathode, grid, and plate. Those tubes because they were not intended for RF may not all be uniform in respect to construction.

Yea, that's the main problem is having an identical pair, I have at least 4 or 5 of them in a box in my stash, and I think only 2 of the 4 or 5 are identical.

[KE6DF]

I've never seen one in RF service, only in class C as TV horizontal sweep amplifiers (fundamental about 100Khz) and in medium voltage power supplies as pass regulators. 160M and 80M sure, but at some point there may be issues. Compare the interelectrode capacitances to RF tubes like the 6146 and also look at one visually to best consider the internal inductance of the connections to cathode, grid, and plate. Those tubes because they were not intended for RF may not all be uniform in respect to construction.

That's a good point.

I've noticed with 6BG6's, particularly the straight sided GA versions, that some tubes have the elements near the base with the whole top part of the envelope empty.

Other tubes have the elements near the top of the envelope with very long leads up from the base.

One would think the tubes with the elements near the base would be more stable in RF applications.

Use the high up element tubes for audio.

A low element example:

http://www.ebay.com/itm/One-NEW-CHANNEL-MASTER-brand-Japan-6BG6GA-tube-07-/260999617184?pt=LH_DefaultDomain_0&hash=item3cc4ca1aa0

A high element example:

http://www.ebay.com/itm/Radio-Tubes-6BG6GA-6BG6-RCA-Test-98-93-PAIR-/350556135668?pt=Vintage_Electronics_R2&hash=item519ec620f4

The 6CD6's of different brands also show the same differences.

dave

[KM1H]

QST had an article about sweep tube modulators around the early 60's and the 6GJ5 years. Likely a McCoy article iffn I remember and a few types were tested.

Carl

[VE3AJM]

I know that Nick VE3OWV has used triode connected 6146s as modulators in his DX100. It sounded good.

[WU2D]

In my experimenting I have found what the other say is true, 6146's, 807's and 1625's all make excellent modulators as long as you bias them right and use the right iron and a little feedback.

[Jim, W5JO]

Why would you choose tubes that are scarce and expensive?   The 6DQ5 is the least expensive sweep tube I have seen so economics makes it a good choice, but how long will that last?

[VE3AJM]

I see 6DQ5s nos at hamfests in Ontario for reasonable prices. So if you had a bunch of them already it might make sense to use them. I do remember working Les W1FAT sk in the 80s and he used them as modulators in his modified Johnson Valiant. He used a S9 driver transformer with the arrangement.

[The Slab Bacon]

6DQ5s are bas-ass! At least as far as all of the octal based sweep tubes are concerned. Several on here have had sucess with them as modders. They also are good as RF finals all the way up to 10m. The Gonset G-76 uses one as a class-C modulated final making 50w of resting carrier, and the Hammarlund HX-50 SSB transmitter uses one as a linear final at 50w of slop bucket.

Just FWIW......................

[W4AAB]

The original article using the 6GJ5's and the 6GW6's as zero-bias modulators was by George Hanchett, W2YM in February, 1962 QST. Lew MoCoy had an article later in that year adapring the "Novice Gallon" to plate modulation with a similar circuit.

[kb3ouk]

RCA datasheet for the 6146 says use fixed bias in modulator service, cathode bias is not recommended. Wonder if that might be what gave the 6146 a bad reputation as a modulator tube, people trying to use cathode bias on them?

[KM1H]

The original article using the 6GJ5's and the 6GW6's as zero-bias modulators was by George Hanchett, W2YM in February, 1962 QST. Lew MoCoy had an article later in that year adapring the "Novice Gallon" to plate modulation with a similar circuit.

I guess my memory is holding up better than many my age

My GSB-100 also uses a 6DQ5 and sounds real nice on AM thanks to it being a phasing rig.

Carl

[WU2D]

6GJ5's - Yup those were early sweep tubes and I think that was what was in my old NCX-3.

[Opcom]

Why would you choose tubes that are scarce and expensive?   The 6DQ5 is the least expensive sweep tube I have seen so economics makes it a good choice, but how long will that last?

6DQ5's and 6CD6's would last for 5-10 years in a TV set. How many hours a year was put on a TV set back in the day?

I've noticed with 6BG6's, particularly the straight sided GA versions, that some tubes have the elements near the base with the whole top part of the envelope empty.

Other tubes have the elements near the top of the envelope with very long leads up from the base.

One would think the tubes with the elements near the base would be more stable in RF applications.

Use the high up element tubes for audio.

A low element example:

http://www.ebay.com/itm/One-NEW-CHANNEL-MASTER-brand-Japan-6BG6GA-tube-07-/260999617184?pt=LH_DefaultDomain_0&hash=item3cc4ca1aa0

A high element example:

http://www.ebay.com/itm/Radio-Tubes-6BG6GA-6BG6-RCA-Test-98-93-PAIR-/350556135668?pt=Vintage_Electronics_R2&hash=item519ec620f4

The 6CD6's of different brands also show the same differences.

dave

Well that's it. Now the audiophools will be 'selecting' those tubes.

Using audio forums and usenet to compound their general ignorance in such matters, they'll come to desire the ones best suited for RF as appropriate for reproduction of "airy highs". Shortly thereafter, the tube vendors will begin devising the appropriate eBay prattle.

[Opcom]

RCA datasheet for the 6146 says use fixed bias in modulator service, cathode bias is not recommended. Wonder if that might be what gave the 6146 a bad reputation as a modulator tube, people trying to use cathode bias on them?

In my experience, the closer the screen grid is run toward its maximum voltage rating or dissipation, the more potential there is for overheating problems in cathode biased circuits. I never ran them with cathode bias.

[The Slab Bacon]

Hmmmmm................

In the old days of 6DQ5s, 6DC6s, 6BG6s, etc they were called "horizontal output tubes". Somewhere later they became known as "sweep tubes"? ? ? ? ?

Kinda like "at what point does a large boat become a small ship? ? "     

[k4kyv]

I think the term "sweep tube" originated in ham circles as slopbucket gained a foothold, and in CB circles as "leen-yars" came into vogue.  In the TV industry they remained "horizontal output tubes" for as long as hollow-state TV technology was used.

[WBear2GCR]

I have a Valiant II that uses 6DQ5s in the modulator.
It was built up by Dave KE1AV, Tim HLR may recall what went into it.
It makes over 100% modulation, no problem. Has the 3 diode neg peg limiter.
Should you hear me on the air, I am running that rig.

Kicks butte, imo.

The thing about sweeptubes (from "horizontal sweep") is that they are good for a ton of peak current.
More than something like a 6146 or EL34.

Very good for modulators, and in a smallish package too.

                        _-_-bear

[W9BHI]

I would really appreciate it if you could find the information on the change to the 6DQ5's.
The diode limiter info would be cool also.
Thanks,
Don W9BHI

[Steve - K4HX]

Three Diode Negative Peak Limiter info here.

http://www.amwindow.org/tech/htm/3diodeka.htm


From the Valiant mods article

Brent, W1IA has gone one step further and swapped the 6146 modulators with type 6DQ5 TV sweep tubes. You will need to rewire the tube base to do this but it will give you much more audio punch from the tubes. You will probably want to change the meter resistor in the cathode circuit of the modulators to a value of .202 ohms. Do this by cutting it in half & butt splicing into it with some copper hook-up wire so you can reconnect to the tube socket. It's made of nichrome wire & will not solder. Your meter will now read 500 mA full scale. This is needed to measure all your new audio punch.

The entire article and schematic are at the link below.

http://www.amwindow.org/tech/htm/valiant/valiantmods.htm

[Opcom]

I think the term "sweep tube" originated in ham circles as slopbucket gained a foothold, and in CB circles as "leen-yars" came into vogue.  In the TV industry they remained "horizontal output tubes" for as long as hollow-state TV technology was used.

Depending on the date and the technical level of the discussion, they have been called many things.

I make no claims. What is the order of propriety?

horizontal deflection amplifier
horizontal output tube
horizontal switch
H.O.T.
sweep tube
trace amplifier

?what else?

I always called them "horizontal output tubes" to customers.

"sweep tube" is vernacular but the term may have been first used in "ham tips"-like publications. I think it's slang from tube designers or application engineers writing application notes.

It may have then been seized upon by ARRL handbook authors who assumed the term was proper because of its origin and the majority of whom cared little for the tubes' noble service in television sets.

The use of "sweep tube" in association with an RF application implies that the speaker means the high powered horizontal deflection amplifier, not the small vertical deflection amplifier.

What was the earliest date the term "sweep tube" was seen in a publication?

If it was first coined by a vacuum tube design engineer specializing in products for magnetic deflection applications, would that legitimize it?

A tube by any other name would still glow as bright.
-Rosie Playt

[WBear2GCR]

on my Val i ain't the modulator section was completely bulldozed and replaced... new iron too... fewer tubes...

                  _-_-bear

[IN3IEX]

WBear !!  Tons of peak current  at very low anode-cathode voltage is fine for class C too !! But this is another story.
In Italy we say: "do not touch that key".





~~~~~ class E?  ... sorry,  my alphabet ends at class C~~~~~~

[WU2D]

Beautiful article this month in Electric radio on a 6146 Class AB modulator. 6SJ7, 6J5 and a pair of 6146's for 100 Watts. For those of you who do not get this fine mag, bang head with soft 813.

[W4AAB]

I found the article about the 125 watt modulator using push-pull 6146's. It is from April, 1958 CQ Magazine.

[WA1GFZ]

6146s lived in many SSB finals. A linear RF tube should be fine at audio.
The 6DQ5 has twice the peak emission so it will haul more peak current.
I ran a pair as switch tubes in my V2 PDM rig for many years and the tubes never got tired.