The AM Forum

I need some input from the ol wise ones. I am shopping for a different AMP. I have two options presently.
A) Gonset GSB-201MKIII with new power supply and 572b's
B) Heathkit SB-221 with softstart, meter and fan mods.
My issue here is one of cost of tubes. I can replace all four 572's for the price on one single 3-500z. I know the owner of the sb-221 and he was a very heavy smoker. but the amp has been out of his hands for about three years. The current owner runs the sb-221 on 120vac which I will do also  and it reportedly produces 800-900W when not drive hard.
The Gonset is owned by radiojunkyard and is original execpt the power supply.
I'll drive with a FT-102 so softstart or something will have to interface to the Gonset.
Give me your input, cause I need about 150-200w carrier to be heard around the southeast.

Get the Heath and put extra air on it.
Good tubes will last a very long time if not abused.If you are really thrifty a pair of 4-400s works in there by denting the R.F. compartment lid for the extra height and directly grounding the grid pins.

I second the Heathkit 221.  I have an SB220 that I've ABUSED for years, ORIGINAL 60s Eimac's in it, and I just started having a rash of caps going out (well, one had been going out for the 15 years I've had the amp, I just didn't know it / recognize it).

FWIW, the caps in mine that went out where ALL bypass or padders, and all where 'doorknob'.

My 'opinion' of the 572 is that it's a hotrodded 811A.  Plain and simple.  Others have agreed.  Based upon that, for AM service, I've told people to run them between an 811 and 572 specs, figuring about 100 watts diss per tube.

Doing the math that way, you get an extra 600 watts of diss on the Heath, and a similiar KVA power supply.

--Shane
KD6VXI

I have an SB-220 (built it as a new general in 1975) and a GSB-201 MkIV and either will comfortably run around 200 watts carrier output, they will both produce more but I think that is pushing it too hard.  My SB-220 still has the original Eimac tubes in it and will produce around 1200 PEP output on 75 loaded and tuned using the original tune up on CW and switch to SSB HV technique.  It was retired from heavy usage in 1999 but prior to that it spent a lot of hours in contest and DX service.

Between the two I would select the SB-221 as my first choice but the Gonset wouldn't be far behind.  The Gonset power supply is very substantial and I have used it a couple of times on AM.

With the SB-221 plenty of airflow is the key.  Many of us ran it with the outer case removed and an additional fan aimed at the power supply area to help it stand up to heavy contest use.

the sb-221 has never been used in contest mode, just rag chew. It has the fan mod done to use a larger fan. I'll be running it on 120vac so 900w would be max in an unpushed mode. It alread has the soft start and a standby switch added to the rear, why there I'll never know.

Power from the SB-221 depends upon the capability of the 120 volt feed you are able to use.  With up to date wiring and a dedicated 20 amp 120 volt feed using at least 12 (preferably 10 for reduced voltage drop) gauge wire allows the SB-221 to be used at full rated power. 

The other extreme is an older house with only 15 amp service to the entire room in which the radio is located.  Allowing a couple of amps for lighting and other misc use and 4 amps (assuming smaller/fairly efficient) for the other radio gear only leaves 9 amps for the amplifier which will limit it to to around 800 watts input with around 500 (125 watt carrier) output since you have to allow for power drawn by filaments and fan along with transformer loss.

In any case you won't see much over 60% efficiency and it will be lower as you go up in frequency.  My SB-220 will produce 1200 watts PEP on 75 implying that I could run it at 300 watts carrier output with normal 100% AM modulation.  But I don't think either the power supply or tube cooling would stand up long under those conditions so I think 200 watts carrier output is a safe limit.  Of course you could treat it like a drag racer and do a major rebuild after every run but if so you better sign up CPI and Harbach as sponsors  :)

I have a dedicated 20A line to supply the amp with #12. But I tend to run light, I am planning on 150-175W carrier, only what I need to be clearly heard.

I would jump on the SB-221 for that kind of service. A pair of 3-500's will handle AM at that level all day long for decades.

Either of your amplifier options will run happily with long life at that power level.  

If you go with the SB-221 check the connections at the filament choke and at the tube socket.  This is heavy gauge wire and if the original builder did not have the proper soldering equipment the connection may not be well soldered.  Also take a look at the cathode connections of the socket and at the tube pins themselves for signs of severe heat discoloration.   If there isn't enough tension on those parts of the socket a lot of heat will be generated and in a few cases the pins have gotten hot enough for the solder to melt out.

Nothing less expensive for 1000 watts of plate dissipation than a pair of 3-500Zed's

I might pick the SB-221 also, but consider an advantage of the Gonset.

The Gonset power supply is full wave with a transformer center tap, and a large negative lead filter choke. The Heath uses a full wave voltage doubler. So for 120V usage, the Gonset has an edge here since the AC 120V current will be sinusoidal , and full 360 degree conduction whereas the Heath will draw large current spikes for just a fraction of each line cycle.

So comparing these two rigs, both on 120V, the Heath will cause more line voltage sag, and more waveform distortion (flattened voltage peaks). Put the heath on a stiff 220v circuit, and wow everything tilts in favor of the Heathkit.

Both will do 200 watts AM all day long, and the Heath will do more, maybe 250W (?) before the power supply gets too hot. The 2 X 3-500Z tubes are good for legal limit though.

Jim
WD5JKO

Thanks to all of you for your input, I have decided to go with the heathkit.. I think with all of the mods and updates i will be happiest with the 3-500z's

1000 watts of diss in a 1200 watt linear is an AMAZING difference compared to the 4-600 watt diss of the quad tuber.

It's also been said.....  If you need more than one tube, you need a DIFFERENT tube.  :)


--Shane
KD6VXI

Are you limited to the current choice for some reason?  Frankly I am not wild about the Heathkit amp for AM.   I don't know anything about the Gonset, other than what's been posted here.  Do you need 160 coverage?  Since you are running a 102 you don't really need a modern amp with a tuned input and an older Henry or Drake L4, L4B would be much better except you don't get 160 with the L4 (it might be possible to add it with a mod, not sure).  Now that I think about it the SB220 didn't have it either.  I guess my point is if you want to go the amp route, to realize its advantage (some real suds like 300 w. at least) you need a godzilla h.v. supply and a lot of cooling.  The older amps have both with the tubes in chimneys.  If you are okay with 150 w., maybe a plate modulated rig like an ART13 would be a possibility, then you are not into all the complexities of driving an amp. 

p.s.  Cheapest 1 KW plate diss. is used 4-1000A hi hi.

Cleaning the Heath of the smoker's residue is something of a consideration.

I'd probably remove the front panel and the meter, and run the chassis sans tubes through the dishwasher. Then ur several days on a radiator or a very low temp oven bake to get the xfmr dead dry...

There are some time I think in the handbook section now - and former thread on getting the smoker off the rig...

                                   _-_-bear

the current owner has done the smoke cleaning, so I'll just have to check the usual clips and connections out before putting in the pubs.

Good choice on the Heathkit. It was made in such quantities there will always be parts and help around for decades.

When 3-500's become scarce there will still be many NOS surplus 4-400's to chose from. Directly ground the grids and use a low profile plate cap as in the Ameritron AL-82 and its plug and play.

Carl
KM1H

Well if it can go wrong it will, just received an email from the sb-221 owner, he dropped the amp while moving it to ship. Broke tubes and meter, no telling what else. So back to the Gonset or ???. I'm limited to 120vac @20A in the house and wife said no to pulling cable into the retreat we share. Bummer.
So besides the gonset I have been offered a Hammerlund hxl one, but it is only two 572's. I don't think it will do 200w carrier and has some paracitics issue with it's tuned input.
Any other suggestions... bummer

The GSB-201 is a fine choice.  Although the 3-500Z tubes have more Pd I have more faith in the Gonset power supply.  Maybe after the poor design of the GSB-100 transmitter power supply they decided to get it right with the amp :)

I wouldn't hesitate to buy the Gonset.

Do hams seem to have a higher percentage of klutzes than other groups? Im always reading of someone dropping things.....especially tubes :o ;D

Id still hold out for another Heath; the same basic amp comes as the SB-220, SB-221, and HL-2200. For not much more $$ look at the Kenwood TL-922/922A

Carl

What is your spending limit?   Can you get to hamfests?   Although it takes patience and I realize that is not easy, maybe by dragging your feet you might turn a disappointment into a blessing if something good comes along later.  that's too bad about the SB221 but I've had things like that turn out to be good later on.

Carl,

The hams must not like the TL-922 amps as much in your area, they seem to be made of precious metal down here in IL.  I found one at a hamfest last year for a good price (I wanted to pair it with my TS-820S/R-820)  but many of them seem to break the 4 digit mark before they change hands.

The Drake L-4B is another to keep an eye out for, it uses a pair of 3-500Z tubes with forced air cooling via a blower and chimney system and a fairly rugged external supply.  They seem to sell for a little less than the SB-220 (no idea why) and a lot less than the Kenwood.  The earlier L-4 is the same except it uses 3-400Z tubes which are hard to find but with new chimneys you can use 3-500z tubes.  The L-7 adds coverage of 160 and uses the same power supply as the earlier Drakes but it drops the blower/chimneys and uses a fan like the SB-220.   The Henry console amps are nice also.

There are regional price differences Roger but I didnt expect it in your area. I often have people asking if Id like to buy their 922 for $750-900. I have bought several at the low end to convert to 6M when the no coders destroyed the Heath prices.

Carl

They are definitely cheaper up your way Carl.  I found mine at a small fest.  I just missed an HT-33B (which I would like for my SX-115/HT-32B station) at the same fest. 

The L-4B is especially nice because of the external amp. You can build your own hot rod supply with out any hassle.

Give us your impressions of the R-820. You can start another thread, since this one is about amps. I've never seen an R-820 or talked to anyone who admitted to owning one.

whatever amp you get for AM look at the loading padder caps.  I am now learning the hard way that cheapie disc ceramics are no good for AM even if they are rated for 2 or 3 KV, they don't like the duty cycle current.   There are a lot of little bugaboos in ssb amps when used on AM but the L4 series with the big separate supply and chimney cooling addresses two of them.

thanks folks, lots of good info given, I am looking hard at the Gonset. As mentioned is does has a 360deg sine wave load. The power supply has been reworked, so relible supply. It fits where I need it to and I can pick it up at a hamfest. What's not to like...