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Author Topic: Whatever you do dont put B's in there (6146B's) and the HW101..  (Read 17757 times)
KE4JOY
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Posts: 1418




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« on: November 03, 2010, 09:31:30 AM »

I read that stern warning here and on other sources.

The finals in a HW101 designed to 6146A's 'will not neutralize with B's'.

Then I read some success storys about sucessfull use of B's in a 101. Then I read that there was a run of B's that were actually A's that were mislabeled  Huh

So I threw caution to the wind, plucked a pair of B's out of a 401 parts box and with great intrepidation swapped them out for the existing ones in the 101. Why? Low drive from 21Mhz and up. Yes the HFO, mixer, etc have all be checked.

Fully expecting a time consuming and lengthy neutralizing process I fired up the rig with the B's in it and checked the neutalizing. Hey pretty close... wait a minute !! Its right on !  Shocked

Dident have to tune anything they swapped out like a set of batterys  Grin

I guess I'm just lucky I fully expected to have to spend some time tuning but did not. Oh and the output went up accross all the bands about 10%. Full 80+ watts on 10 meters  Grin

Guess Im lucky !
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G3RZP
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Posts: 1284




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« Reply #1 on: November 04, 2010, 01:11:28 AM »

I ran 6146Bs in my HW101. In fact, I never ran anything else. At the time, where I was working, I had a large supply of 6146Bs, so there was no problem in supply and no problem with operation. I even ran it with 1150 volts on the plates and about 200 watts output!
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KG6YV
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Posts: 593




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« Reply #2 on: November 04, 2010, 06:59:46 AM »

I have owned the HW101, SB101 and SB102 in the past.  All are basically the same/identical from the standpoint of the transmitter circuit through and including the final amplifier.  Never had a single issue neutralizing 6146B's. 

The 6136B was introduced far earlier in the 1960's than any of those radios.  I first saw an SB101 in 1968 and shortly thereafter the ads for the HW101 came out.  I have QST's with RCA ads for the 6146B from 1964.

The caution is valid for transmitters/transceivers that were introduced in the early 60's like early S/N KWM2's, Collins 32S1's and the like.  Even Collins changed their neutralizing cirauit with a service bulletin in 1964. 

Another 'urban myth" busted! 

Congratulations for having courage,

Greg
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WB6RXG
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Posts: 73




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« Reply #3 on: November 04, 2010, 01:44:10 PM »

I ran 6146B's in my HW101 for years without any problems whatsoever.

I seem to remember it as a common upgrade for the Heathkits.

They seemed to last a little longer than the A's.

73,
Stuart
WB6RXG
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K8AC
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Posts: 1905




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« Reply #4 on: November 05, 2010, 07:22:35 AM »

The 6146Bs have a higher plate dissipation (35W vs. 25W) than the 6146s and could handle 33 1/3% higher input.  To run them at the higher input, the screen voltage should be increased from 160 to 200V.  Never had any neutralization problems using them in Heathkits or other transmitters that I converted from sweep tubes to 6146s.
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WQ2H
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Posts: 28




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« Reply #5 on: November 19, 2015, 08:11:42 AM »

I ran 6146Bs in my HW101. In fact, I never ran anything else. At the time, where I was working, I had a large supply of 6146Bs, so there was no problem in supply and no problem with operation. I even ran it with 1150 volts on the plates and about 200 watts output!

Imagine that. De-rating. There's something you rarely see any more.  Smiley
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WA5VGO
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Posts: 74




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« Reply #6 on: November 20, 2015, 09:27:13 AM »

Ordered my HW-100 in 1968 right after they came out. I was put on a waiting list. When it arrived, Heathkit supplied it with RCA 6146B tubes. There was a card enclosed that said RCA couldn't meet their demand for 6146A's so use the B's in their place. The 6146B tale is nothing but a myth.
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G3RZP
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Posts: 1284




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« Reply #7 on: November 20, 2015, 02:31:00 PM »

There are well authenticated claims that certain Motorola and Collins rigs couldn't use the B's. As far as Heathkits and other ham rigs are concerned, I never had a problem - BUT YMMV! But I might be surprised in such a case....There's possibly less problem at HF than at VHF.

The professional rigs I did we checked out with straight 6146s with no problems, although we did wind the drive back. Not everywhere in Africa could you get 6146Bs in a reasonable time scale, but 6146s could well be in stock somewhere in the country.
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JS6TMW
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« Reply #8 on: November 20, 2015, 04:14:30 PM »

and with great intrepidation swapped them out

The best mashup word I've come across in ages!
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KM1H
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Posts: 5289




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« Reply #9 on: November 20, 2015, 06:14:19 PM »

By the time the S Line was mature the fix to use the B was well known, the early problems was poor component engineering/choices. Collins was far from perfect.

Motorola was a royal PITA to service as they often had their own specs for tubes and had the tube companies produce them and assign specifc numbers. In reality an off the shelf tube worked fine but any authorized service facility could lose it if an audit found a non Moto badged tube was used to save the customer considerable money.

I did moonlighting for a local independent 2 way shop and used regular 6883B's to replace the 6883/6883A or Motos own # in VHF sets with no problem. Since most of the customers were taxi cabs who never shut up the B lasted a lot longer!

Carl
Carl
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K6BRN
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Posts: 1293




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« Reply #10 on: November 24, 2015, 08:28:31 AM »

Have to vote with the crowd, here.  Ran 6146B finals in my HW101 with zero problems - very robust.

Didn't help with the HW-101's "Drift-O-Matic" VFO, though. Wink

Brian K6BRN
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KD8SAV
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Posts: 16




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« Reply #11 on: November 24, 2015, 07:42:49 PM »

I'm using a new pair of Chinese 6146B's every day in my HW-101 - and no problem once I got them neutralized, good output.
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K9AXN
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Posts: 442


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« Reply #12 on: November 29, 2015, 08:03:45 PM »

Collins problem with the 6146B was the neutralizing feed back cap would melt because the 6146B needs more feed back to stabilize the tube.  Wouldn't happen with the 6146.

Difference between the 6146 and 6146B is the geometry of the B leans more to a triode than the 6146.  Delivers significantly more output in AB1 mode. Takes more neutralizing to stabilize it and more bias for the same idle current as the 6146.

Before you say case closed, check all of the bands in your multiband radio for neutrality.  Just because it's neutral on one or two bands means nothing for the rest after installing a tube that needs notably more feedback to stabilize it.     
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G3RZP
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Posts: 1284




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« Reply #13 on: November 30, 2015, 06:45:55 AM »

James, K9AXN,

Quote
Collins problem with the 6146B was the neutralizing feed back cap would melt because the 6146B needs more feed back to stabilize the tube.

Do you know what the mechanism was that it needed more feedback?

Looking at the data sheet nominal grid plate capacity

6146    0.22pF
6146A  0.24pF
6146B  0.22pF
6146W 0.24pF

which doesn't suggest a big change. They all have the same mu g1-g2 and transconductance.

I suppose one difference could be the base sleeve and its screening effect, which maybe changed from the 6146 to 6146B and even to some 6146As.

Or was it something to do with circuit and layout?
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K9AXN
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« Reply #14 on: November 30, 2015, 04:23:45 PM »

Best answer is to measure the bias needed to idle the 6146 then the 6146B.  Then note how much feed back is required to neutralize the tubes.  The data sheets can only tell you what the mean cg to p capacity is.  Haven't found any tetrodes where the cg to p capacity doesn't vary markedly throughout the inventory or even the batch.

The mechanism is the geometry of the elements i.e. how well the screen shields the cg from the plate.  Effects both the idle bias and cg to p capacity. 

Mark the adjustment position of the feedback cap that you use to neutralize the tubes using the 6146.  Then insert a 6146B and neutralize it.  Measure the capacity of the feedback cap for both tubes.  Do the same thing with a number of 6146B's or 6146's.  The variation is easily measured between and within tube types.  It's a good indication about the range of values for the mean values quoted in the data sheets. 

If your cap meter doesn't measure below a Pf, take a look at the Tonghui series --- they're not prohibitively expensive and measure to a ff.

Regards
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