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Old 5th October 2017, 03:18 PM   #691
w5jag is offline w5jag  United States
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... including a 1 Kilowatt tube amp. I already have the necessary parts for these projects ....
I guess this is another one of those deals that takes a while to sink in .....

How are you planning on doing it? Tetrodes? Couple of 4CX1500's? They have a lot tougher screen grid than the 4CX1000. I'm guessing they could be driven with a receiving pentode like a 6AK6 .....

I once had aspirations of building a compact kw out of a pair of 4CX250B's, but then lost interest and sold/gave away all of my 4CX250 stuff. I ran across a couple more sockets a while back, and still have the case I intended to use. I think I may still have a PT in the warehouse of junk. Yes, that is real copper sheet metal .....

I don't have any RF tubes bigger than 572B's, except for some 4-400 pulls, that may or may not be any good ......

I'm thinking low power for my SPP build. I want to make a complete FM receiver, and I have this LMB Heeger cabinet in stock. The bottom chassis has plenty of room for the solid state stuff, most of which still needs to be built, but top side will be tight. An SSE board will just fit transversely, but the little bit of extra width on the SPP makes it longitudinal only. I've had this in the back of my mind for a while, which is why 6G6 went immediately into the push pull test mule with the psuedo SPP front end. I'm thinking 6AK6 for the power tubes - should be able to get 2-3 watts without a lot of heat to dissipate.

Getting a power supply into the cabinet, OPT's, etc., and dealing with the generated heat will be challenging. I have some ideas, unconventional, don't know if they will work. I want to use a one box solution - no external power supply, if possible.

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Old 5th October 2017, 07:26 PM   #692
mkane77g is offline mkane77g  United States
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Where did you get that copper box?
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Old 5th October 2017, 07:48 PM   #693
w5jag is offline w5jag  United States
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HamComm - Dallas, TX. 'Bout a decade or more ago .....

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Old 6th October 2017, 03:54 PM   #694
Tubelab_com is online now Tubelab_com  United States
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How are you planning on doing it? Tetrodes?
I abandoned, and sold most of my big RF tubes years ago. The reality is that an OPT capable of the voltages and impedances that big RF tubes want, are out of my price range. I still have a few 833A's, a plate transformer out of a Harris transmitter, and an SE OPT suitable for a guitar amp (but only one) so I may build a big guitar amp some day.

I lucked into some "surplus" Plitron P-P OPT's several years ago that are 1250 ohms, 400 watts at 20 Hz and suitable for a high quality HiFi amp. The usual suspects for these OPT's are 6 to 8 KT88's, but I will use TV sweep tubes, probably 36LW6's or 35LR6's.

Currently looking for a suitable chassis, but again, progress has stalled due to the usual reasons. I spent the entire day on the phone yesterday trying to transition from the ACA to Medicare while leaving Sherri on ACA. No success, trying again today, currently about 40 minutes on hold again.
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Old 6th October 2017, 05:10 PM   #695
w5jag is offline w5jag  United States
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Originally Posted by mkane77g View Post
Where did you get that copper box?
You know, I hadn't looked at that bad boy in more than a decade.

But sitting here at my desk over lunch, looking at the picture of it, I bet it would hold a couple of SSE boards modified for push pull with 6146's, independent power supplies for each board, room for the fm tuner / preamps / tone controls, etc., and more than ample front panel space for meters, frequency display, etc .....

And I pretty much have all the major parts on hand, including OPT's with a third winding for the screen grids or cathodes .....

It might even fit in the small space where the child resistant SSE now sits. Width and height would be OK, I think, not certain about the depth, but I think it would fit ....

I've never tried to work copper sheet metal. I assume it is softer than aluminum or steel?

Food for thought ......

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Old 6th October 2017, 06:29 PM   #696
mkane77g is offline mkane77g  United States
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Old 6th October 2017, 07:16 PM   #697
Tubelab_com is online now Tubelab_com  United States
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A lot of the old "copper" chassis from the 60's were really copper plated steel. A magnet will tell the truth.

I ripped apart some old RF sweep generators for their tubes and power transformer. The nice copper chassis turned out to be plated steel, but I saved one anyway. It didn't make the move up here though.
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Old 6th October 2017, 11:08 PM   #698
w5jag is offline w5jag  United States
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A lot of the old "copper" chassis from the 60's were really copper plated steel. A magnet will tell the truth. ....
A PM speaker wouldn't stick to it at the time, and I just had a known good refrigerator magnet slide right off it, so it could be copper plated something, but I don't think it is steel ....

Best I recall the fellow had several of them, and said it was copper, but that was a lot of hamfests ago. I believe the early R.L. Drake tube type radio chassis are copper, rather than copper over steel, but I haven't put a magnet to one.

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Old 7th October 2017, 05:59 PM   #699
Tubelab_com is online now Tubelab_com  United States
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I have never seen copper plated aluminum so it may indeed be solid copper. Weight could be a clue too.

I vaguely remember seeing some copper looking chassis in my younger days, but most copper looking consumer chassis were steel based for economics reasons. Some old TV sets (Zenith maybe) had selectively plated areas where component leads were soldered directly to tabs on the chassis.

Somebody's old HiFi chassis were copper, but I can't remember who. Don't think it was Fisher, maybe Pilot? The Pilot Stereo 70 watt amp that I had in the early 70's was gold painted steel as was the cage.
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Old 8th October 2017, 04:38 AM   #700
w5jag is offline w5jag  United States
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I believe it is solid copper. It feels like copper, and I pulled one of the screws out, and it looks like copper all the way through.

Metallurgy aside, the good news is that it is small enough to fit under the TV; the bad news is that it is small enough such that the footprint of two SSE boards, and two of the Merit OPT's, takes up pretty much all of the volume of the cabinet.

It's still do able, I think, but would be more complicated than I anticipated just looking at the pictures over a tuna fish sandwich. I'll have to layer stuff in the cabinet.

I have a pair of identical flat pack R-Core power transformers that can power each board to about 60 watts input. I can put a sub chassis on top of those for the amp boards. That should give me abut five inches of vertical height left - about what I've already managed with the child resistant SSE, so anything that has worked there, would work here. That covers quite a bit.

These PT's are less than ideal for 6146's; I would have to double them for B+, and regulate a screen voltage out of the undoubled output. Probably no room for chokes, so multiple FET ripple filters will likely need to be built. Probably will have to mount a vertical partition to mount all of that power supply circuitry on.

It would need to be force cooled, so some thought to airflow through it would be needed.

I can remove the bells, and lay the OPT's flat, and mount a chassis above them to hold the tuner, input switching, tone controls, low voltage supply, etc. It would have been helpful if the tuner I've already built was about a half inch shorter in it's longest dimension. I'll probably just build out the rest of the solid state receiver stuff to be compatible with either chassis, no real need for a decision just yet.

45's should fit, barely. Have you made a push pull TSE? Maybe one 5842 in the front end driving a MOSFET as a phase splitter, then to the followers?

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