The AM Forum

this is kind of a shady looking spec sheet, ( didnt know the Irish were in the tube business ) but I thought I would ask anyway. who's used em as modulators?

hi Derb ...may be more relabeled Chinese stuff .... on a quick glance specs seem in order .... on you huskeys !!

Hi Derb,

Just viewed your YouTube video; very cool and enjoyable!

Looks like you've collected some nice parts and rigs there, OM. I look forward to hearing and seeing more as you progress with these various homebrew projects you are working on.

With regard to the 572Bs as modulator tubes: I knew a fellow that used a pair of them to plate modulate a single 4-400A. He had a Heath SB-200 linear amplifier, which used the same tubes, and his logic was to maintain commonality of tubes for sparing, etc. The modulator provided plenty of audio to fully and cleanly modulate that 4-400A, which was running about 750-800 watts DC input. He used a 150+ lbs RCA broadcast type 900777 250 watt modulation xfmr that I had given him; 15K ohms P-P, to 5030 ohms on the class C side, with no mod reactor. The rig sounded superb. I think he may have used a separate PSU for the modulator (lower B+ than the 4-400A final), but that was 30 years ago, so my recall may not be accurate.

Of note; the 572Bs he had used in that rig were the (probably now unobtainium) United Electronics (UE) original production tubes. I believe the current production 572B is from China; I have no idea as to how the reliability or performance of these tubes compare to the UEs. As a generalization, some Chinese tubes are better than others in that regard; I have had excellent luck with the Chinese Shuguang 845s for example, as class-A drivers to my 833A modulators, but I have heard of other users having less satisfaction with some other Chinese power and transmitting tubes. The Shuguang 845 is built like a battleship, and probably just as good as the old-stock U.S.-made 845s.

73,

Bruce

A 1965 Data Sheet copied from the Chinese??? What a joke! ::)

The 572B was originially designed by Taylor c1963 as an audio tube called the T-160L. Poor timing as AM was on the way out so they convinced Heath to try it at RF and sold the rights to Cetron.

That data sheet was from a rebrander hoping to score on the SSB craze. Its a bit optimistic for modulators at 2500V and it also requires around -3V bias at over 2000V. At 700W of old buzzard AM the plates get quite red.

Amperex, Raytheon, GE, Cetron and United all built the 572B in the US. Plus there were several rebranders and OEM labeling (Dentron, Hunter, etc)

Carl
KM1H

572Bs have the 6.3V 4A (25.2W) 811A thoriated tungsten filament structure, with 175 watt plate dissipation (I have seen claims of 225W) compared to the 811A at 65W plate dissipation.  15Kp-p suggests high B+, and the 811A emission supported 340 watts from a pair of 811As at 1500V.  So I would expect a pair of 572Bs would be able to modulate an 800 watt transmitter with substantial reserve, assuming 2000 to 2500 plate volts.

Emission limits plate current, and plate dissipation and other things effectively limit plate voltage (how much resting current can the tube take, also efficiency will be like 60% so how much output can it produce even with no resting current, etc).  And we get away with a lot because of the intermittent characteristic of speech.  With 175 watts (or more) of plate dissipation, 572Bs can do a lot more than 811As.

But the spec for these 572Bs... hmmm.   810s, with more powerful 10V 4.5A (45W) thoriated tungsten filaments, had a similar spec, although they need -70 volts or so of bias at 2500V, and they were only rated at 725w audio output.  In modulator service, I would think more like 500 watts max from a pair of 572Bs by that kind of spec, if you want long life out of them.  But at 2500V, I am sure you could get 700 watts from them new.  Their lifespan would be a matter of duty cycle.  With a low duty cycle, they might last... with a heavy duty cycle, hmmm.  And we tend to run a heavy duty cycle, especially when fighting QRM.

The data sheet IS from 1965.  Seems optimistic.  AND  these guys cannot seem to spell Zirconium .... makes one wonder.  Think that these specs were for Class C modulators -- useful in the Criminal Band ...  oopppps .

GL  Vic

Sure. Why not. People have run a pair in SSB service at 600-800 watts output for decades. Modulator service is no different.

Ive converted over 250 SB-200's to 6M monobanders and the much increased efficiency of getting rid of the poor input circuit and other switching allows an easy 800-900W out key down even with full output Cetrons that are 30-40 years old. BUT after about 45 seconds of that the plates start to show color. This is at around 2200V under load and 700ma Ip. Obviously this is pushing them and the PS way too hard but the tubes have the emission to do this. Chinese tubes will run the same power but show color faster. 

I insert a series R with the drive to cool things down a bit before shipping.

Carl
KM1H

Those SB200s are sleepers. They may be the best deal dollar per watt ever. A few mods and they are rock solid.

I wish I could find whomever made the 572B's in my Dentron DTR 1200L because they are the only tubes that can provide a power gain of ten-to-13.

The No-name tubes I received with the Amp and the Svetlanas I had on hand only provide a power gain of about half that of the Dentron tubes.

My tubes start redening at about 300 mA plate current (150 mA each tube) at 2100 volts Vp.   

Hmmm, I wonder if the Irish tubes glow GREEN? :o

Phil - AC0OB

Power gain in dB, or max saturated Pout?

--Shane

Years ago I used to have a new pair of 572B's just waiting for me to get my license and start building.

 ??? Time marches on, I don't have them, not for a long long time.

"Amperex, Raytheon, GE, Cetron and United all built the 572B in the US. Plus there were several rebranders and OEM labeling (Dentron, Hunter, etc)

Carl
KM1H
"

The SB-200 I obtained a couple years ago had a pair of Sylvania 572B's.  The plates barely blush after a long key down on AM.  One of them rolled off my bench and went south when I was installing a new Harback P.S. board so I ordered a pair from China.  The Shuguang 572B's from China blush a bit more much sooner but still seem to hold their own and work fine. 

I have a brand new pair that I bought about 2 years ago. Actually, I had bought a quad for a Gonset GSB-101, but a friend needed a pair, so I sold him two. Figured I'd just put 811A's back in the 101, so I've got the 572B's and thought about building them to modulate the 2x 813's. Do you think an ART-13 mod tranny would stretch that far?
Phil   

I used a sb200 back in my 'before AM' days. worked VK and ZL on 75  using that and a butternut HF 6V with 40 or so radials under it. I guess 1984.

'Twas the Siltronix 1011D for me, Derb. With the 8950 mod. Similar results to Europe circa 80-82. Had a little Sonar BR-something with swep tubes in it for local work back in the 70s. Traded it off to another high school radio buddy.

I run a quad of Cetron 572Bs in the 30L1 desk amp in place of the 811As not for any more power out, but for 24/7 durability. The thing just loafs along. A lot of folks seemed to believe they could gain a couple hundred watts with the trade not realizing you need to have the power in as well as components designed for the additional load before you can get the power out. For me, it was more like swapping out 4-250s for 4-400s.

Can't speak to the newer production versions, but the older 572s were killah!

I don't find the 572 claim outrageous for ICAS. After all, you can get 100-120W from a par of 25 watt 807's in the zero bias triode circuit. If the specs were advertised for a sound reinforcement or music application, I would be suspicious because of a high duty cycle. design philosophy. reduced cost and weight or standard cost and weight. Worry about the 572b performance when the FCC starts allowing ham band music.

• Worry about the 572b performance when the FCC starts allowing ham band music.

Running 20-25 dB of compression gets their knickers tight also ;D

The wimpy fan in the SB-200 can be replaced by the Harbach, especially for Chinese tubes. In a homebrew a 4 1/2"  muffin fan is mo betta.

Carl
KM1H

I had a linear with a pair then bought two more to make it a quad. I lost interest after my first trip to W6 land when I bought a new engineering sample Penta 4-1000A with cap and socket at HRO for $22.50....this was around New Years 1974.

the P-8033  plate xfmr I have is rated at 1700 or 2000 @ 675 ma ICAS.  :D

The power gain of the Dentron 1200L averages 8.5 dB over 80 to 10 m.

Now I have to locate a two-position wafer switch for the Standby-Transmit switch.

Phil - AC0OB

1200 watts out from a quad of Svetlana Russian 572s in my Collins 30L1. Been in there for 10 years.

Thats impossible with the stock PS.

Carl
KM1H

Maybe it's Dosy watts.

Is there any advantage to using 572's in place of 811's in a linear amp designed for 811's  other than probably lasting longer and a higher price tag?

• other than probably lasting longer and a higher price tag?

One offsets the other. In a 30L1 the 572 will last forever especially when pushed on 10-15M. Same thing in other vintage 811 amps that are running at their maximum voltage/dissipation especially during tune up.