Heathkit Station

Discussion in 'Amplitude Modulation' started by KA5SDC, Apr 23, 2019.

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  1. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Look at the difference in price for the Mullard 6CA7 between the 2-sites. The first wants $25.95 and, for a new one, the 2nd site wants $249.98 for a "standard" version and, if you want one with a brown colored base, the price is $449.95! Even a used "standard" Mullard is $119.95!

    Mullard was one of the original suppliers to the Heath Company for the 6CA7 tubes. Since those tubes were already being used in the hi-fi equipment, I suspect that Heath was getting a very good price on the tubes. Therefore, since they were cheap, and would do the job, they were used in the Apache modulator stage.

    Although I have not tried the lower priced 6CA7 tube brands that are featured on both sites, I believe that they would hold up fine as modulators in the Apache especially since the relative time spent with high voltage on the tubes is short. Remember, unlike when used in hi-fi amplifiers, the only time that any voltage higher than the heater ("filament") voltage is applied is when actually transmitting.

    Glen, K9STH
  2. AC0OB

    AC0OB Subscriber QRZ Page

    I have a pair of Svetlana EL34's (6CA7) in mine and they modulate very well.

    I replaced the fan with a 65 cfm fan and taped the RF cage with aluminum HVAC ducting tape to suck in the air from the side and out the top.

    I also have the Mohawk with some minor mods and they are both are reliable rigs.

    Here's some mods I made to my Apache:


    Attached Files:

    Last edited: Apr 25, 2019
  3. K4KYV

    K4KYV Subscriber QRZ Page

    Was that the "list" price, or Allied's actual selling price? There used to be a standard "list" price for tubes that was exactly double the real price. Kind of like Sears & Roebuck tires that were always on sale at a substantial discount from a fake regular price. The "list" price is what was always posted at radio & TV repair shops, so they could charge the customer an inflated price and he would still think he was getting a discount.
  4. N2EY

    N2EY XML Subscriber QRZ Page

    Actual catalog price. Mullards were premium imported tubes back then too....in the USA, anyway.
  5. W6RZ

    W6RZ Premium Subscriber QRZ Page

    Be aware that the fairly inexpensive "new production" Mullard tubes are really from Russia.
  6. KE4OH

    KE4OH Ham Member QRZ Page

    Indeed. Mullard, Tun-Sol, and maybe other brands from the past have been purchase by current tube manufacturers and jobbers and applied to new tubes. This does not mean that these tubes are bad. Many new production tubes are quite good. However, don't be fooled into paying NOS prices for a newly manufactured tube. Caveat emptor!
    AC0OB and KD2ACO like this.
  7. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page


    There used to be a group of AM operators in the Texas, Oklahoma, Arkansas, and Louisiana area who operated every morning from before daybreak until around 9:00 AM local time on 3880 kHz. Several of the regular participants were VERY critical of the signal quality of other operators. Most of these operators had oscilloscopes, etc., connected to their receivers so that they could visually look at the signals as well as determine quality "by ear". Sadly, a number of those operators have passed in the last several years.

    When I first "checked into" the group, with my then unmodified Apache, they, basically, "tore me a new one" (posterior) because of the "tinny" quality of the audio. After a few days of receiving the abuse, I took a look at the audio circuitry in the Apache. There were 3-each capacitors that caught my eye. Of these, 2 were coupling capacitors of very low capacitance and the 3rd was of which I considered proper value but was a disc ceramic type. I replaced these 3 capacitors with "orange drops" (because those were what I had in stock, other similar "poly" capacitors will work fine) and then just unplugged the 6AL5 "clipper" tube.

    The next morning, I checked into the group. All of the operators, who had been the most critical of the quality of my audio, gave me rave reports. They could not believe that it was the same transmitter and when I told them what I had done, they were astonished at how simple the modifications actually were.

    Since putting the information on my website, I have heard from a number of operators who made the same modifications and who also started getting excellent reports on the quality of their signals.

    The schematic for this modification is listed in post #14 in this thread.

    I did not switch the audio gain control and the clipper control. The audio gain control is still behind the key jack. The fact that this control is not located on the front panel, and the clipper control is labeled "gain", presents a problem to those who acquire the Apache transmitters used. They assume that the gain control is what adjusts the modulation level and it really controls how much clipping happens.

    The microphone that I use with my TX-1 Apache is a plain old D-104. It has one of the very last Astatic manufactured replacement microphone cartridges that were available direct from Astatic. This cartridge was obtained several months after Astatic stopped manufacturing these replacement cartridges. The microphone that I use with my WRL Globe Champion 350A, Heath DX-100, and Hallicrafters HT-20, along with all of my tube-type SSB equipment (Collins S-Lines, Heath SB-Line units, Eldico T-102), has a Kobitone 25LM022 cartridge that produces excellent audio with transmitters that require a high-impedance microphone. Unfortunately, this cartridge is no longer available.

    Glen, K9STH
  8. WA4JK

    WA4JK Ham Member QRZ Page

    Glen, I was one of the gang on 3880 with the east Texas bunch, Mike, Richard, Geoff.... so I know what you mean about very critical of anything they did not approve of or that threatened their superior view of themselves....But we had fun. I think Ken has the 833 HB rig of one of the group. Don't know where the 304TL rig is that one from one of them from Dallas. I found out the purchaser had no clue what he was doing inside a transmitter. Most are gone now, but a few of us still plug along.
    AD5HR likes this.
  9. AD5HR

    AD5HR Ham Member QRZ Page

    3880 is where I "cut my teeth" on AM operation.
    Otis(K5SWK) with his homebrew 833 rig, Perry(W5KGZ) with a Globe Champ 375 or BC-610,
    Goeff ( W5OMR) with the "Titanic",2-250THs modded by 2. and Scotty (K5SPE) on
    his homebrew 2-833As modded by 2, and myself with a Globe Chief 90 and homebrew
    plate modulator.
    SWK and KGZ are sadly SK, the others are still active.
    On 3890, it was the N.Texas,Okla., and AR group with K5BAI as M.C.
    3890 has the Texoma AM Traders Net every Sat. morning at 7:00 Central time, and at times
    will have 30 or so check-ins. (cues up the old tune "Memories")
  10. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page


    KGZ had a WRL Globe Champion 350. The last Globe Champion made was the 350A of which I have one of, if not the very, last of that model manufactured. My 350A has the flat front cabinet like was used on the 300 (not the "shadow" type normally on the 350 and 350A) and the front panel has the "A" added with "press on" lettering and not silk screened. However, the circuitry is the latest, and greatest, 350A version.

    I was in contact with Leo Meyerson not all that long before he died. When asked about the transmitter, Leo explained that, after the 350A was discontinued, the company received several orders for that model. Well, Leo wasn't going to turn down business. So, they started looking around for all the physical parts like front panels and cabinets. However, there were not enough of the "shadow" cabinets to completely fill the order and there were not enough front panels that had the 350A on them. So, as the factory ran out of a certain part, they just used one from an earlier model with the last 2, or 3, having both the 300 cabinet and the "A" added to the front panel!

    Some CBer tried to modify the VFO to cover 11-meters not realizing that, even though the calibration for 11-meters is not on the dial, the VFO already covered that band. This person made a mess of the transmitter and an amateur radio operator out in Oregon got hold of the transmitter. He heard that I was looking for a Globe Champion and said that I I paid the shipping, he would give the transmitter to me. Shipping was about $50 at that time. When it arrived, the VFO was certainly mangled and a couple of the coils were wiped out. I was able to find the remains of a 300 VFO, which was the same circuit as the 350A and replaced the broken coils with ones from the 300 VFO. The transmitter then worked fine! It has some paint missing on the front panel, but, otherwise, the transmitter is in excellent condition.

    Oh, one of the AX9909 tubes was broken by the CBer. So, I made the modification that was in Electric Radio a while back converting the the finals to 5894 tubes. Since that tube is designed for VFH, I actually get about 15-watts more output, for the same input, as when the AX-9909 tubes were in the unit.

    Glen, K9STH

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