The grand old 6146 - I'm asking some serious questions about this device.

Discussion in 'General Technical Questions and Answers' started by KD4HNC, Apr 9, 2019.

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  1. KD4HNC

    KD4HNC Ham Member QRZ Page

    Hi om's. I have several Heathkit rigs. They were gifts, with the advice that they did not work just right. I tried to use a couple on the air, but they didn't work or tune right. I like tubes in general, although I have several solid state rigs as well, such as I-coms among others. I liked the Heathkit so much, I decided to buy several more for parts, from ham fest & Ebay, to rebuild one to perfection. While I intended to use one or more for parts, none of them were cheap by any stretch. I decided not to scrap the original two gifted rigs, & progressed to rebuilding the best condition rig acquired from Ebay. Along with the purchase of the rigs, I bought from another ham on Ebay, two said to be new old stock, JAN 6146W, manufactured by Philips ECG, with slightly different date codes, one is 8626 aau, 26th week of 1986, the other is 8652 aax, 52nd week of 1986. While both were sold as new, these tubes have getter flashes, both of which appear to me to have been used, as the flash shows signs of gas absorption in the flash pattern. When I tested them with a dynamic transconductance tester, both readout were 125%. That alone told me something wasn't right. Generally tubes with damaged grids test high on my tester. Tubes that are really good/new always test 100% So onwards to the present, I have finally found the time to restore one of these Heathkits, with the chassis restocked with new high grade caps, & all the mods including the preselect tracking mod for xmit/rec tuning point. I tracked the vfo to a precision, dead on readout across the band, put shields on all of the tubes, & proceeded to install the two ECG 6146 listed above. Right away I knew there was something wrong. The original tubes were a pair of RCA dark cathode types, with no getter flash, telling me they are high vacuum tubes, unlike low vacuum tubes that use a getter flash to absorb the remaining air from the envelope. The AB1 bias point on the RCA's was set by me before swapping tubes, & was very stable over several weeks of testing. When the ECG's were installed, the bias setting was way off, & resetting the bias to the ECG tubes, I could get only about 60% CW power out, or 60 watt, while the RCA's gave me 100 watt output. I also noted a drop in stability. After several seconds, the PO began to drop below 50% or 50 watt CW output. I suspect now, the original owner did not properly dip the plate current during tuneup, & from long winded use, burned up the screen grid, (causing warpage in the focus of the grid) Now comes the questions. The rig was possibly produced 50th week of 1968, stamped in large black ink numbers on the chassis, making it possible the RCA's are the original output tubes, which by the way work great! I also suspect the ECG's are not dark cathodes, due to the tremendous difference in the filament current, between the two odd types. Since there are two filament circuits, some 12v some 6v in series parallel, including bulbs, it crossed my mind the ECG's maybe are not getting hot enough, or back to my first thought, they have the damaged screen grid. My tube tester compensates for different filament currents with a 100 to 130 volt ac adjust, to be set after the tube warms up, by slowly increasing the current, ie; starting from the 130v setting & reducing the setting until the line cal is met in the center of the meter. At this point I have no idea, or guess, weather or not the ECG's are really bad? Now the final question. Does anyone out there know, or have experience with this issue. Is it a circuit mismatch, a damaged pair of tubes, or both? Please reply even if you just have a hunch or guess, I will weigh all comments equally.
  2. KE0ZU

    KE0ZU Ham Member QRZ Page

    Perhaps paragraphs are in order here.
    WA8FOZ, K0OKS, AE8W and 7 others like this.
  3. KE4OH

    KE4OH Ham Member QRZ Page

    My thoughts:

    • Buying any tube as new from eBay or anywhere else is a crapshoot. Maybe it is, maybe it isn't.
    • Your knowledge and your tube tester are leading you to believe that the Philips tube grids may be damaged. Maybe you are right.
    • Sometimes, even new tubes are bad. Rare that both would be. IF they are new ...
    • 6146 control grid is the weak spot in an otherwise very tough tube. Running greater than 3 ma grid current per tube for a long time is a death sentence.
    • Output falling off? Could be gassy tubes.
    • Output falling off? Could be a weak driver tube.
    • You sure you have the bias / idle current set correctly? It has to be set each time you re-tube. Heathkit SB- and HW- series need 50 ma at idle, with mode set to LSB or USB, mic gain fully CCW. Idle current will be slightly higher in CW mode.
    • So, what rigs do you have? We all want to know!
    • Your post was very hard to read without paragraphs.


    Steve KE4OH
    KA0HCP and N2EY like this.
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I've purchased "NOS" 6146-series tubes from RF Parts, who offers a warranty on everything. Half of them have been bad right out of the carton.

    They took them back and replaced them and continued doing that until I had all "good" ones.

    Pays to buy from a distributor/reseller who offers such a warranty.
  5. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Yes, your post is VERY hard to read! Please use paragraphs.

    All that aside: Most of the Heath equipment is VERY unhappy with the 6146B / 8298A or 6146W tubes. Those tubes are different from the normal 6146 or 6146A / 8298.

    Heath did get a special "run" of tubes for the later HW-101 units that are marked "6146B". However, those tubes are really 6146A / 8298. There was a note included in the kit telling the builder not to use any other 6146B tubes in the unit.

    You can use the original 6146, the 6146B / 8298, and the 6293 tubes in the Heath equipment as "plug and play". Sometimes you get lucky and the individual unit works fine with the 6146B / 8298A or 6146W. However, what it takes to neutralize those tubes is different from the original series and that may require modification to the transmitter. Many of the older equipment, that was designed for the original 6146 or 6146A / 8298 are very unhappy with the 6146B / 8298A or 6146W. I have run into situations with identical model of a specific unit, with serial numbers within 10 of each other, where like 1-unit was happy with the newer tubes but 2-other examples were very unhappy. There are people who say that they have never had problems using the newer tubes and I believe them. However, my experiences have been different.

    The article, on the 6146 family of tubes, that has been widely published in a number of amateur radio magazines (even internationally) as well as numerous newsletters, etc., can be found at the following URL:

    Of course, there will be a couple of participants who will come on and say that the article is "bunk"! They have had no problems or they have been able to modify the equipment to use the newer tubes satisfactorily. However, over the years, I have had several hundred persons contact me saying that the problems with the newer tubes is real. But, again, I definitely believe that there are people who have had absolutely no problems with the newer tubes. My experience has been with, literally, tens of thousands of the 6146 family of tubes so the sample is a "bit" larger than that of most people.

    Glen, K9STH
    KC8VWM and KE4OH like this.
  6. W9WQA

    W9WQA Ham Member QRZ Page

    yeah,cant read wow, wall of words. and id like to read his stuff, i like tooobs! too..
    i often do each sentence,space. ez to read
  7. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Merit Arnold, the guy who owns RF Parts, seems to agree with you and via telephone has given me strong advice about which 6146s to use in various pieces of gear, including Collins.
  8. KM1H

    KM1H Ham Member QRZ Page

    Tens of thousands in AB1 linear mode ham gear which is what this thread is about??????? Excuse me if I have doubts.

    Ive no experience with the Collins or Moto FM issues but with dozens of AB1 Kenwoods, Hallicrafters, plus Class C use in Heath, Johnson, Gonset, Knight, and others Ive yet to have a problem, even with a mix of the two types just to see what happened. This is not the first time Ive mentioned that to you.

  9. KP4SX

    KP4SX Premium Subscriber QRZ Page

    K8AI likes this.
  10. KD4HNC

    KD4HNC Ham Member QRZ Page


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