The AM Forum

Pair of 6DQ5's have been used for some modulators for 100 watt class BA rigs.
For a plate voltage of about 1000vdc or so,
and a screen voltage of around 150v.  What could you expect for the useful power output ?????

Thanks,
Jim

http://amfone.net/ECSound/Valntmods1.htm

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

Zero after the first buzzard xmission.

500 volts would be better. Look at the normal tables with tube types of similar plate dissipation for a good yardstick.

ROFLMAO

Check the spec for SSB linear service. That should get you pretty close. IIRC, a pair of 6DQ5 are rated for 24 watts plate dissapation or almost 50 for a pair. This should give you something like 100 watts in AB1/2 service.

Thank you Steve (Mr. Disruptor)    ;D  & Dave
I remember Timtron sayin they (BIG sweepies w/their high gain)  will modulate the pizz out of a Valiant/Dx100 etc.

811a's are beckoning...but than you gotta drive them......

You can also run most of those sweep tubes in triode connection too.

Timmy was refering to some of the later generation "sweep" tubes Like 6LQ6s or some of the even more strapping ones (I dont remember the numbers) used in last generation biggie color sets. These are well suited for the junkston rigs as they are fairly low impedance tubes with tons of emission and will make copious power at lower plate voltages. thatz what ya want to look into.

6DQ5s were strapping tubes in their day, but wont hold a candle to some of the last generation sweep tubes. In the days of 6DQ5s they were refered to as "horizontal output tubes", the later ones were refered to as "sweep tubes" ;D ;D

                                                          the Slab Bacon

I think the 6MJ6 was the strappiest of them all as a last generation sweeper.

I checked the 6DQ5s in my pdm rig about two years ago. after 20 years they were fine running 1550 volts in switch mode with cathode drive. Just keep an eye on dissipation in AB. I got the most monkey swing with about 60 volts on the screens. At zero g1 bias the modulator current will peg the meter. I think it will take at least 60 volts on the cathode to cut it off. G1 bias voltage might take a bit more to cut off. Triode connected will reduce the gain at high voltage.

6CD6 is even better, and cheep too. But don't tell the audiophools! I better quantify that statement.

I quote me: "The 6CD6 horizontal-output-type beam power tubes are certainly more robust than the original 7581's, in fact, they are rated at 200 milliamperes plate current which is far more than the 7581's 74ma, and even beats the 6550's 175ma. The 6CD6 uses 2.5 amperes for its 6.3V heater, and this was a concern since the 7581 uses only 0.9 ampere. ... The 6CD6 uses relatively low screen voltages, only 180V as compared to 350V for the 7581"

I am in favor of tubes that will draw high currents with low G2 voltages because this allows more plate voltage swing without excessive dissipation in the screen grid and the associated drainage of cathode current in high peaks to the screen, depriving the plate and hastening clipping.

An excruciatingly pleasant to listen through 50W amp conversion is shown here:
http://www.montagar.com/~patj/aph1050.htm

The nicety of these tubes is the very high average cathode current available. The output was not really limited by the tubes but by the amp chassis voltage and iron used in the project.

My recollection of the deal with sweep tubes is that they will handle probably 2x the rated plate voltage and will put forth a snotload more current than they are rated for in the book... up to the point where you burn holes in the plates.

The only problem with that scenario is that "back in the day" they were about 2-3 bux each, and easy to find. Not so today. So, it might make sense to run them somewhat conservatively.

I have a pair in the Valiant II, mod by Dave KE1AV, it was his rig at one time, and it pins the modulation current meter on peaks no trouble. Stock B+ on it. 6BQ6, iirc. I think.

Should be able to pull ~200 watts on peaks out of a pair of them, the only question is for how long... imho.

                  _-_-bear

Speaking of TV tubes, has anyone tried building a modulator with the beam power triodes color TV pulse regulator tubes?

I'm talking about 6jd5, 6jh5, 6jk5, and 6hz5 and their ilk?

These all have similar plate dissipation ratings to the larger sweeps (e.g., 35 W) and similar high current sink capabilities.

And they are cheap

I nominate teh 20LF6. 40 watt plate dissipation, temp overload of 200 watts, put air on them and the munky will swing 360º in a circle.

yes, the fil voltage may present problems.

500 ma avg cathode current, 1200 ma peak. 990 plate voltage maximum. swing.

oh yeah. this link be most useful.


http://www.shinjo.info/frank/

Thanks for responses.
<the rest of the story>

I'll need copious amounts of audio because longer term (when I'll actually have time to work on this junk).  I want to swap out the 6146's in the Rf section and put in either a pair of 4-65's (expensive)
or 814's (cheap  :)  ) This rig (DX100) would now be a  200w med. power xmitter. 
Half the fun though is just pouring over data sheets to see what would fly...with the existing plate iron.
SS power supplies & cap input for the audio: about 1100 vdc for either BIG sweepies or 811a's.
Rf would get about 1000vdc after the voltage drop from reactor chokes (modified heising).


http://www.mif.pg.gda.pl/homepages/frank/sheets/049/8/814.pdf

Unless you sub mount teh tube sockets, I'm not sure the 814's + plate cap will fit. If it's a DX-100B, I'm pretty sure it wont. Them suckas are tall.

   In  1992 I mudifyed My DX-100, when finished it consistently delivered 200 watts carier out with modulation peaks of slightly over 1100 Watts.  Few believed me of course and Carl WB1EYE and his friend Lou asked if they could visit me with their calibrated Autek peak Watt meter. They gently told me that they did not want to drive from eastern Massachusetts to Almost the New York border and visit me if I was doing the normal Ham Radio exeragation/Bullfertilizer entertainment thing. I laughed and asked them to bring me some drunkin doughnuts up from North Adams, Ma after sliding down the famous hairpin on the Mohawk Trail on route 2. 

    I let them hook their Autek into the 52 Ohm Dummy load and they sat on the bed when I loaded up on 3885 KHz  They agreed that the carier was about 205 watts and when I spoke theysat forward and when I whistled they jumped up and jumped for joy. They each spoke into the D-104 and make Yellows, etc.

    Well they departed home for the 3 hour and 15 minute drive and ordered 36LW6's or the more expensive lower filament versions. My 36 LW6's cost $4 each from Antique Radio Supply and I lit the two in the RF Final and Two tetrode connected modulators with an old Torrid xfmr from a large satellite dish actuator.   
    The scuttlebutt is on my HamElectronics.com   Shortly after Tim, hlr and Gary, inr started experimenting with Lw6's.
     In RF service their combination fixed/self bias requirements are no where near a 6146.
 Regards  John   

I found alot of stuff there, but could not find the DX-100 mods. Can you provide a direct link to it?

   The mods apply to most any low or medium power transmitters, not just the Valiant or DX-100 I protyped with.

here is a page  http://hamelectronics.com/k1deu/pages/ham/transmitters/am/pages/modulation_power_mods.htm
and
http://hamelectronics.com/k1deu/pages/ham/transmitters/am/pages/universal_speech_amplifier.htm

   For modulating the DX-100's 200 watt carier to 1130 PeP, I use a Dynaco Hi-Fi 30 watt audio output xfmr primary only, with 800 VDC through a 1 Meg resistor on its case. The transformer shell/case being 800 volts above chassis is supported/insulated with a 1/8 th inch lexan bracket. The LW6's run very cool with 1100+ VDC on the plate caps and 20 Ma. Quiescent per tube. The transformer shell/case is supported/insulated with a 1/8 th inch lexan bracket. In the Valiant I cross-laminated the original modulation xfmr using a 3-2 pattern for more primary inductance and did not use an insulating bracket.  As there isn't any modulation xfmr ratio (only the primary coil is used), the higher plate voltage on the modulator tubes along with their maximum current ability determine the modulation PeP.

   After 3 days of heavy transmitting, only the stock DX-100 plate transformer is hot, the Valiant transformers run warm only! The pi-net out put tank is re-done on each band for the new PeP.  Regards  John

Thanks very much!

What about the real old 6BG6? I like the classic shape of those.

The 814 ( VT-154) is one of my favorite sleeper tubes. Another is the 4D32/4D22 for lots of power at low voltage. Im thinking the pulse rated 3E29 is no slouch either with a pair in PP parallel. The audioholes havent ruined them yet.

Carl
KM1H