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All my meters swing forward, receiver swings backwards

Discussion in 'Amplifiers' started by groundwire, Oct 17, 2020.

  1. AudioShockwav

    AudioShockwav Extraterrestrial Admin
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    The reason I asked about voltage drop is I ran across a large hand built amp that the performance was lacking, it would hold a fairly good dead key, but struggled to produce peak power.
    A voltage reading at the collectors revealed that there was considerable voltage drop at that point when modulated hard.
    The power source had plenty of reserve, the wiring in the amp however was lacking.
    I have to agree, even though the Toshiba's could take some abuse, probably better to run them gently now days.
    I have no experience with the new Hg's so I don't know if you can beat them up like the originals.



    73
    Jeff
     

  2. 543_Dallas

    543_Dallas Sr. Member

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    I had decent luck with the gs35b tubes that I bought. I've bought 6 good ones from ebay and 2 duds. The duds came from sellers in the US and I suspect they knew they were bad. I could have done a better job conditioning the tubes. I would run the heater for 24 hours and give them 4kv.

    I have one that arced over twice and popped the fuse in the amp. I finally cooked it long enough that it held 4kv. With the amp keyed the bias current would pull the plate volts down a couple hundred volts which was just enough the tube didn't arc. I left keyed for several hours and got lucky. I still cant believe that tube survived.
     
  3. 144inBama

    144inBama Electricity doesn't kill you, ignorance does.

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    Everything I've seen from a "sensible" approach from builders says they can handle hard swing, just not volts i.e. over 16VDC or a high dead key... not continuously anyway. The guy who built my amp has posted 2 videos on how to run the HGs. He said you can run them any way you like, and he'll be happy to take your money to replace the blown pills, but if you want it to last, use the 25 watt per output transistor and keep it under 16VDC. Donkey Stomper and BBI both pretty much agree on this method.
    But simply put....No, you can't whoop on em like you could the Toshibas. Now, if you were to treat the HGs like you had the last set of transistors in the world, and they were DEIs, it should last forever and a day.
    Again, this is just going by the builders recommendations.
     
    groundwire and Tokin like this.
  4. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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    Interesting...all mine sez' this...
    upload_2020-10-18_9-25-33.png

    I tend to agree with the Consensus of the negative swing - you're mods are placing too much effort on Dual-Sideband - with little carrier to support.

    It would fit the facts, you get less received carrier - the farther away the receiver is, so the signal in the remote receiver may see it more like a FM or SSB signal ,"fluttery" with not enough carrier to support the needles desire to track the swing than the detected carrier. They see it as "Backwards" because the audio rises, but carrier "falls" - possibly sounds pretty distorted or fuzzy on narrow filter AM strips,

    They may hear you just fine in Wide AM receive, but as the carrier power gets weaker, the means to decode or detect the information, your audio, is less and less presence in which to work with..
     
    NZ8N and 144inBama like this.
  5. snippits75

    snippits75 Well-Known Member

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    From experience with a 2 pill HG2879 at 14.5 volts.

    Forward swing on average scale at 50 watt carrier. Around 55 to 60 watt carrier swings backwards. Running mine now at 20 watts per transistor for a total of 40 watt carrier.
     
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  6. 144inBama

    144inBama Electricity doesn't kill you, ignorance does.

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    Like I said... Some like it rough other don't.. LOL.
    My 1X4 takes a 100 watt DK beautifully, it will take a 200 watt DK with maybe 10 watts forward swing in avg, both swinging the same PEP. I get more audio with the 200 at distance "locally" but no difference in DX so I of course run the 100. I'm only hitting it with @18 watts PEP out of the radio. If the HGs have been hit hard, they get weak pretty quickly which will cause backwards swing as well. God I miss the Toshibas.. :(
     
    Shadetree Mechanic likes this.
  7. snippits75

    snippits75 Well-Known Member

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    Hit the 2 pill with 35 PEP, and the transistors dropped 100 watts over a period of two weeks talking here and there. Had the two transistors taken out, and the Hfe was at 4 on both of them. Put a pair of used HG 2879 with Hfe of 16 into the amp, and the power came back up. Driving the used pair with 20 to 25 watts PEP, and they are holding up way better than the new ones did.

    I miss the Toshibas too. The HG's work, but from my experience so far the Hfe drops like a rock if pushed just a little bit. With the age and prices of sweep tubes going up and up, $30 a pop for transistors is not that bad to play CB!
     
    #52 snippits75, Oct 18, 2020
    Last edited: Oct 18, 2020
    Shadetree Mechanic and 144inBama like this.
  8. groundwire

    groundwire Sr. Member

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    Ok so i readjusted all my levels and its all forward swing now. Carrier at 400w and she swings foreword. At 300w carrier it swings forward even better. So i guess 300w carrier swinging 3200w it is. Lol, those numbers seem crazy (such a huge power swing) but i guess thats the way she goes
     
  9. Slowmover

    Slowmover Elmer

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    From, the agony of defeat, to, . . the thrill of victory!
     
  10. Handy Andy

    Handy Andy Do Your Research First, Then Decide...

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  11. Shockwave

    Shockwave Sr. Member

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    All of mine came from Russia and took a while to arrive. While you've seen that you can find good ones, the trouble I had was finding 3 that would work anything close to balanced, together. With only 4kv on them, I cannot even begin to count the number of internal tube arcs that would trip out the "Triode Protection Board".

    Good glitch resistors and lightning fast protection got one year out of that amp before two 3CW7000A7's went in with a pole pig. In 7 years, those two Eimac's have never arced once or even skipped a beat! Where the 3 GS-35's almost wore out the protection reset button on the front panel. On the other hand, it is nice to hear you had some luck with them.

    PS: I've also never seen a triode so hungry for grid current. Each can draw 400ma and all three were pulling a whopping 1.6 amps of grid current! With such fragile grids, this is not a good position to have to run them in.
     
    #56 Shockwave, Oct 18, 2020
    Last edited: Oct 18, 2020
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  12. 144inBama

    144inBama Electricity doesn't kill you, ignorance does.

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    My very 1st amp was a 2 pill 350 HD (2X2879). Then I started driving it with a 1 pill (2290)....THEN I started driving a 4 pill (4X2879) with both of them. Radio was literally 1/4 watt DK swinging 20 into the 3 boxes. I was getting around 900 screaming watts...bleeding 120 channels on every band there is. talking on toasters, irons and pretty sure the washing machine (I don't do that any more...) but the point is, people said I couldn't do it without blowing the pills so I had to show them, it was all in the swing. I finally did blow the 4 pill after 2 years of abuse @18VDC. These were all Toshibas so that should tell you how durable they were. We'll probably never see the likes of them again.
     
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  13. 543_Dallas

    543_Dallas Sr. Member

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    Mine was only a single tube amp. It didn't have a grid current meter so I had no idea they pulled so much current. I did install a grid current meter when I put in the pair of 8877s. I was going to use a pair of GS35b in my HF amplifier but decided to go with a 3000 instead. I think they're decent for what they cost and it's not too hard to change over to something else when the surplus drys up. I still see them on ebay but don't know that anyone is buying the things anymore.
     
  14. Shockwave

    Shockwave Sr. Member

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    As luck would have it, the single tube amp is also the ONLY place I had any luck running these Russian surplus tubes. Matching them at this degraded age, is nearly impossible.
     
  15. Shockwave

    Shockwave Sr. Member

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    I will add that the 8877 surprised me. I was able to obtain many pull outs and 3.9 KVA transformers from obsolete Perkin Elmer RF generators. Stacked a pair of transformers on one RF deck and proceeded to push an 8877 to 7,200 watts on the average Bird meter and the tube had the nerve to handle it with only a little bluing on the anode from severe overheating.

    The most surprising thing to me was the transformers were not stacked in parallel here. They were stacked in series and were supplying about 1 volt per watt under load!

    I've also seen 8877's with 1980's date codes on them that were not worth a damn. It is the reason these RF generators were deemed obsolete and the next version used the 3CX1200D7. Your choice of going with the 3CX3000 was the way to go for sure. That tube does not have a fragile grid and can take lots more abuse.
     
    #60 Shockwave, Oct 18, 2020
    Last edited: Oct 18, 2020
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