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Old 9th April 2013, 09:11 PM   #1
tricomp is offline tricomp  Denmark
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Default Compactronized 6146

Hi,

Today I received a quintet of GE NOS/NIB 7984 Compactrons.
I got them cheap from eBay just because, especially just because of the high Pa-rating.
What I didn't know is that they are apparently 6146-clones, or am I reading this wrong?
See the attached page pulled from a GE Ham-News ed.
I'm sure that if I am right then the Genie is out ..and there will be no more cheap 7984's.

rgds,

/tri-comp
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File Type: pdf GE 7984_(6146-Clone).pdf (438.0 KB, 129 views)
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Old 10th April 2013, 01:43 AM   #2
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No, ur reading it right.

But unless ur running the tube for RF service it doesn't buy you much.
First off you need a compactron socket... and 6146s are not expensive.

Worse still is that the 6146 is just not a particularly great audio tube.

But this is still neat if you like beam type screen grid tubes...

Oh yeah, one other detail, 13.5v filament!

_-_-bear
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Last edited by bear; 10th April 2013 at 01:50 AM.
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Old 10th April 2013, 03:12 PM   #3
tricomp is offline tricomp  Denmark
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7984-Curves. Opinions?

rgds,

/tri-comp
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Old 10th April 2013, 03:55 PM   #4
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I have a pair of these which I am toying with the idea of building a spud amp with. I would run them at Va 150V 100mA and use an input transformer to apply parallel feedback ala Schade.
Don't have a clue if it would work yet, but its a cheap and interesting project.

Its not a straight copy of the 6146 having a considerably higher gm.

Curves look horrible in Class A and AB configuration so some sort of feedback seems essential to make it work.

Shoog
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Old 10th April 2013, 04:19 PM   #5
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I had 2 or 3 of these. I didn't think that I would ever use them since I only had a few, so I gave them away. There were several 8156's and 8106's so I kept them.

I have experimented with the 6146 and odd heater voltage variants, and still have a few 6146A's. If you realise that the screen grid limitations are similar to a sweep tube, and treat the 6146 the same way, they will live long and prosper. Wire them up like Ampeg did in the early SVT bass guitar amp and they will blow up.

There was a popular video of a Rolling Stones (Altamont) concert where the SVT burst into flames. Ampeg said that it was because they had plugged 230 volt European equipment into US 115 volt power, yeah right.

I saw an old Ampeg SVT explode into flames, and later on, I got to fix it. It was a 6550 powered model and it fried because the speakers blew, open circuit at full power on a 300 watt tube amp.
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Old 12th April 2013, 04:28 PM   #6
N4BBQ is offline N4BBQ  United States
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Quote:
Originally Posted by bear View Post
Worse still is that the 6146 is just not a particularly great audio tube.
Ouch!
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Old 13th April 2013, 02:37 AM   #7
multi is offline multi  Australia
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How would the 6894 go as a triode; I built an map using 6146 wired as triodes as in the RCA data 400 volts 8k out put transformer, but the tubes where very hard to drive peak Af grid voltage 200 volts. Would the 6894 be easier to drive.?
phil
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Old 13th April 2013, 08:19 PM   #8
N4BBQ is offline N4BBQ  United States
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Quote:
Originally Posted by multi View Post
How would the 6894 go as a triode; I built an map using 6146 wired as triodes as in the RCA data 400 volts 8k out put transformer, but the tubes where very hard to drive peak Af grid voltage 200 volts. Would the 6894 be easier to drive.?
phil
I have a SE 6146-based amp and drive it fine with a 6C4. I am running about 550VDC on the plates and 225VDC on the screen grid. Now this isn't so gainy that will will drive into distortion, but I build them that way to keep the kids from square-waving my system. Its plenty loud enough for me and my darling wife.

My speakers Fostex 166en in a BiB enclosure.
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Old 13th April 2013, 11:37 PM   #9
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Quote:
Originally Posted by tubelab.com View Post
I saw an old Ampeg SVT explode into flames, and later on, I got to fix it. It was a 6550 powered model and it fried because the speakers blew, open circuit at full power on a 300 watt tube amp.
A little off-topic - I just checked a 1970 SVT schematic and was looking at why the amp would have flamed - can you recall where the fire started tubelab? There is a 1 ohm 1W common cathode current sense, and 10 ohm 5W anode stoppers, but they would require serious current to overcook and act like fuses. The only other over-current protection is a 10A primary fuse. And I'm guessing a tube and/or an OT primary shorted in some manner?
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Old 14th April 2013, 01:12 AM   #10
multi is offline multi  Australia
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Default 6146

N4BBQ; thanks for your reply; my problem was the drivers were not capable of driving 200 volts; the amps sounded just like most commercial single ended 300B amps no dynamics and very dull sound. As a pentode the 6146 is easy to drive. Don't see why it is a bad audio tube.
Phil
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File Type: jpg Triode connection.jpg (362.5 KB, 118 views)
File Type: jpg Triode graph.jpg (395.6 KB, 110 views)
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