• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Compactronized 6146

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
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? :Pinoc:
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
 

Attachments

  • GE 7984_(6146-Clone).pdf
    438 KB · Views: 155
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
 
Last edited:
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
 
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.
 
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.
 
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?
 
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
 

Attachments

  • Triode connection.jpg
    Triode connection.jpg
    362.5 KB · Views: 174
  • Triode graph.jpg
    Triode graph.jpg
    395.6 KB · Views: 171
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

Same here; I've built two audio amps using the 6146 as the final stage. They sound good to me. Maybe I'm missing something...?

So Bear, why is the 6146 a bad audio tube?
 
The 807 is the same as the 6146 difficult to drive as a triode, best to use an EL34 triode connected, the 807 is also very easy to drive as a pentode. There are circuits using the 6146 ultra linear but you need to have the ultra Linear windings wound separately with a separate supply, I can not see why the 6146 would be any worse than any other tube pentode with a regulated supply to the screen.
i have boxes full of the 6159 version of the 6146 25 volt heaters. probably i will never use them.
Phil
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.