Car Tube Amp

[w5jag]

Originally posted by w5jag
In the ham radio world, a lot of people complain of short tube life in 6U8, mostly from grid to cathode shorts.

Win W5JAG

I must have had too much Egg Nog yesterday ... I think it's heater - cathode shorts that plaque 6U8 ....


Win W5JAG

[w5jag]

Originally posted by Eli Duttman

How do you propose to convert the "12" VDC in the car's electrical system into the "450" VDC needed by EL34s?

Didn't somebody on this site have a 300B mobile amplifier that used the inverters out of UPS to generate his local AC?

I would probably try an old 12 VDC supply for a tube ham transceiver, because nobody runs a KWM-2, TR-4, etc., mobile these days. I have a half dozen or so of these mobile supplies because you can get them for next to nothing.

I would look for a Drake DC-3 or DC-4 power supply as their rigs used high perveance sweep tubes. The power supplies for the 6146 based rigs would likely have too high a B+ for most common audio tubes.

Win W5JAG

[7N7]

Look, you can buy high-powered supplies these days for peanuts; I installed one not long ago into a Land-Rover so that the owner could run his lap-top on safaris.

This has 230v output at about 3kw - plenty for hi-fi!

7N7

[rcavictim]

7N7 is right. The modern breed of inxpensive, 12 volt to mod sine power inverters are well suited to operate the home type tube amplifiers that many of us enjoy. I have a 1000 watt Xantrex X-Power inverter and it does a pretty good job powering my MingDa Mc34B, P-P, UL 6L6 amp. The amp sounds good but B+ and output power are reduced because of the supply waveform. I suspect one could match this properly in a from scratch amplifier build by selecting a higher voltage B+ winding.

One could spend more and get a true sine wave inverter and this problem would go away.

Many computer UPS systems contain a sine wave inverter. These can be had for peanuts to the watt on the second hand market compared to `actual` sine wave inverters , especially when the inboard battery needs replacing.

[ray_moth]

British Leyland was killed before birth, by first, the stupid incompetent Labour government that conceived the idea (it should never have existed) and second, by that ****** Stokes who ran it. End of story.

That's how I remember it, too. Run by a bean-counter who understood the cost of everything and the value of nothing. It certainly was the end of the story! And yes, he was a w@nk*r.

The 6146 got banged about in many mobile radiotelephones and taxi radios on the 2 meter band (where one tube could make 30 watts RMS FM carrier) and seemed to survive it.

What I meant about the 6146 was that its comact design means that it can easily overheat with the thermal stress of continuous-mode duty, such as in audio amps. It works much better in Class B burst-mode duty, typical in radio communications, where it gets the chance to cool down. Early amps using 6146 were prone to tube overheating and failure. The 6550 superseded it in most designs.

[rcavictim]

Originally posted by ray_moth


What I meant about the 6146 was that its comact design means that it can easily overheat with the thermal stress of continuous-mode duty, such as in audio amps. It works much better in Class B burst-mode duty, typical in radio communications, where it gets the chance to cool down. Early amps using 6146 were prone to tube overheating and failure. The 6550 superseded it in most designs.

My suggestion was based on mechanical suitability. You cannot make a physically weak tube more suitable by turning down the applied power, whereas I see no reason why one could not choose to operate a PP pair of 6146 or better yet an P-PP quad of these (per channel) at reduced ratings so they don`t run away.
That would get expensive though so perhaps other tubes might be more practically suited. I`d be tempted to try the 829B myself with a chassis/case design employing an air filter and a cooling blower. You can use a single envelope with regulated screen supply as a complete push pull package, or two separate bottles for P-P. Option two would allow UL operation from the output xfmer taps.

[Craig D]

Thanks Guys for all your advise and recommendations. Regarding the 12vdc up to the required 420vac, I am currently running tests in my car with a cheap inverter from 12vdc up to 220vac, then to power a NAD 3020. I realise it's not tubes but I was wanting to see if there was any hum or noise and so far none. If it does not work properly with the tube amp, I can purchase a true sine wave inverter but they are quite pricey. Alternatively get the mains transformer for the tube amp to have a higher voltage on the secondary. I plan to power the tube heaters from the 12vdc. Connecting 2 tubes in series. If this is a bad idea please let me know. My reasons are to draw less current from the inverter.
Regarding the output tubes. I could obtain 6146 tubes from the internet as they are not available locally. Are their pins identical to an EL34? Besides the 6146, are there other tubes more hardier than the EL34. Tubes like the 6L6GC, KT88 and 6550 are easily obtainable.
Thanks.

[7N7]

Originally posted by Craig D
Thanks Guys for all your advise and recommendations. Regarding the 12vdc up to the required 420vac, I am currently running tests in my car with a cheap inverter from 12vdc up to 220vac, then to power a NAD 3020. I realise it's not tubes but I was wanting to see if there was any hum or noise and so far none. If it does not work properly with the tube amp, I can purchase a true sine wave inverter but they are quite pricey. Alternatively get the mains transformer for the tube amp to have a higher voltage on the secondary. I plan to power the tube heaters from the 12vdc. Connecting 2 tubes in series. If this is a bad idea please let me know. My reasons are to draw less current from the inverter.
Regarding the output tubes. I could obtain 6146 tubes from the internet as they are not available locally. Are their pins identical to an EL34? Besides the 6146, are there other tubes more hardier than the EL34. Tubes like the 6L6GC, KT88 and 6550 are easily obtainable.
Thanks.

The Sovtek 6L6WXT (also 5881WXT) is excellent and cheap (search ebay) and since these are installed as original equipment in guitar amplifiers I am sure that they would be fine in your car.

7N7