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Author Topic: Drake TR-3 Tubes?  (Read 17221 times)
W3UTD
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« on: February 04, 2011, 05:42:55 AM »

Just grabbed a Drake TR-3 off eBay, it's not here yet, but I was going through the manual and my stock of tubes looking for spares.  The parts list in the manual and the schematic in the manual differ a bit on two tubes:

Parts List       Schematic
6AU6A           6AU6
12AX7A         12AX7

I would guess the parts list would be preferred due to the later "A" designations.  True?  Or does it matter one bit?

73, Fraser, W3UTD
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K9YLI
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« Reply #1 on: February 04, 2011, 06:59:32 AM »

 I dont think it matters.  I was tube trained  back in the 50's.
the letters after ,are just  slight improvments,.

or  GT  after which meant    Glass Tube, as originals were metal tube.
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KA5N
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« Reply #2 on: February 04, 2011, 07:35:07 AM »

The 12AX7A is a "low noise" improvement.  6Au6A has some other improvement.  I wouldn't worry too much about it as you can probably never hear any difference in use with "receiving tube" variations.  You can download data sheets for almost any tube and/or variation.  However if you are not versed in what the specs mean ...  anyway you will usually see that the differences are small and finding NOS tubes is getting harder as the years go by.Many hard core restorers acquire one or more of the better quality tube checkers and check all tubes they buy, be them NOS or used tubes from a swapfest.  Usually it is OK to just try the tubes in the receiver or other device you are  going to use them in.  But ocassionally a tube either NOS or used will have an internal short and may burn up a resistor or too.
Since shorts often show up only after the tube is warmed up, a DVM is not much use in finding shorts. In short either A or non A versions of the 12AX7 and 6AU6 will probably do just fine.
Allen Smiley
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AD4U
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« Reply #3 on: February 04, 2011, 07:48:25 AM »

Vacuum tubes often get a bum rap for failure by people who have never used tube gear.  IMO vacuum tubes are very reliable if used in a properly designed circuit.

I have run tube gear since the 1960's.  Currently I have and use some 30 different tube-type boat anchor rigs.  In the past 50 years I have only had ONE tube fail in receive service or in low level transmitter service.  That was in a Drake R4C receiver.

However in the same amount of time, I have had numerous transistors and IC's fail.

Go figure.

Dick  AD4U
« Last Edit: February 04, 2011, 04:30:35 PM by AD4U » Logged
W3UTD
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« Reply #4 on: February 04, 2011, 08:08:34 AM »

A versions it is then!
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G3RZP
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« Reply #5 on: February 04, 2011, 11:26:19 AM »

Don't the A versions have controlled heater warm up time? I doubt you'll notice the difference. The difficult ones to get may well be the 12JB6s.
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WB2WIK
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« Reply #6 on: February 04, 2011, 11:48:52 AM »

Vacuum tubes oftten get a bum rap for failure by people who have never used tube gear.  IMO vacuum tubes are very reliable if used in a properly designed circuit.

I have run tube gear since the 1960's.  Currently I have and use some 30 different tube-type boat anchor rigs.  In the past 50 years I have only had ONE tube fail in receive service or in low level transmitter service.  That was in a Drake R4C receiver.



I sure agree.  I remember in the 60s when all my ham gear used tubes, every time there was any sort of problem at all, everybody (including me) would start replacing tubes, simply because it was easy and tubes were really cheap.  A lot of receiving tubes were $1.49 to $1.99 or so, so replacing a few was pretty painless, although this rarely ever improved anything.

Now I'm a lot older.

My 75A-4, purchased second-hand in the early 1970s, has every single original tube in it (I can tell because the Collins logo is printed on them) and has probably been used every week since 1972.  They all still work fine. 

Well made tubes are marvels.
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N2EY
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« Reply #7 on: February 05, 2011, 06:41:58 AM »

Don't the A versions have controlled heater warm up time? I doubt you'll notice the difference. The difficult ones to get may well be the 12JB6s.

In the case of small receiving tubes, the A usually meant controlled warmup time. This is very important in series-string heater arrangements, but not so much in a rig like the TR-3.

The finals are the problem, as you pointed out. They're likely to be hard to find and expensive. Ironically, they were used as an economy/availability measure!

73 de Jim, N2EY
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NK6Q
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« Reply #8 on: February 06, 2011, 08:04:11 PM »

The 6JB6 sweep tubes are still available out there.  Antique Electronics Supply has a good inventory of them- you can even ask for a matched set.  Possibly not as cheap as they once were, but a whole lot cheaper than some NOS KT-66 and KT-88 tubes used for vintage Marshall guitar amps.  Now that's crazy.

Bill in Pasadena, NK6Q
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G3RZP
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« Reply #9 on: February 07, 2011, 12:11:34 AM »

Unless my memory is very bad, the TR3 uses 12JB6s, not 6JB6s. They are diddy squat little tubes too, which gives a meachanical problem in trying to swap them for something else. I believe they are a different physical size to the 6JB6.
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WW3QB
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« Reply #10 on: February 07, 2011, 06:20:42 AM »

Unless my memory is very bad, the TR3 uses 12JB6s, not 6JB6s. They are diddy squat little tubes too, which gives a meachanical problem in trying to swap them for something else. I believe they are a different physical size to the 6JB6.

I have a TR-3, TR-4, and a T-4XC. The only difference between the 12JB6 and the 6JB6 is the filament voltage. They are physically identical. The 12JB6/6JB6 is a bit shorter then the 6146, making for a tight fit when that substitution mod is done (I've never done it).

12JB6's are available. There is less demand so they are not advertised much. They are actually cheaper than 6JB6's. Shop around.
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W5RKL
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« Reply #11 on: February 07, 2011, 09:06:39 AM »

Unless my memory is very bad, the TR3 uses 12JB6s, not 6JB6s.

Yes, you are correct. The TR3 transceiver has 3 x 12JB6 final tubes.

The TR4/TR4C/TR4CW transceivers have 3 x 6JB6 and the T4X<any> transmitters have 2 x 6JB6 final tubes.

I agree, the only difference between the 12JB6 and 6JB6 is the filament voltage.


73s
Mike
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G3RZP
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« Reply #12 on: February 08, 2011, 12:16:23 AM »

I've seen some things marked 6JB6 that were much taller - about 6JS6 size. As I recall, they were Japanese or Chinese.....not RCA or GE
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WW3QB
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« Reply #13 on: February 08, 2011, 06:07:53 AM »

I've seen some things marked 6JB6 that were much taller - about 6JS6 size. As I recall, they were Japanese or Chinese.....not RCA or GE

I have a pair of too tall Sylvania 6JB6's.  Sad
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KE4DRN
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« Reply #14 on: February 08, 2011, 03:49:55 PM »

hi,

Tubes are very reliable and have a long life if not abused.
Interesting info on the tubes used in submarine cable repeater systems,

International Submarine Cable Protection Committee

In 1966, after ten years of service, the 1,608 tubes in the repeaters had not suffered a single failure. In fact, more than 100 million tube hours over all AT&T undersea repeaters were without failure.

73 james
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