6CD6GA in Enhanced Triode Mode for SE Amp

[rcavictim]

Originally posted by tubelab.com


I ran the Edcor transformers at 80 mA with 300B tubes for 2 weeks of daily use. No ill effects were noted, and the transformers did not get warm. They sounded good and no saturetion effects were heard or seen at maximum volume (some slight clipping on bass notes).

Tubelab,

Which model and Z Edcor are you referring to here?

Thanx.

[tubelab.com]

The transformers are 5K ohm. I tested 300B's with an 8 ohm load and a 4 ohm load on the 8 ohm transformer for a 2500 ohm load to the tube. I listened to the 300B's for about two weeks with 8 ohm speakers before moving on to trioded 6AV5's and finally UL 6AV5's. I breifly tried 6CD6's since I had several. They can't take the screen abuse that the 6AV5 can. Other sweep tubes will be tortured (oh, I mean tested) in the future. The point is to find the minimum dollar SE amp that sounds great.

The part number is Edcor XSE-15-8-5K.

These experiments have been chronicled across three threads:

There was a thread that introduced the Edcor XSE-15-8-5K transformer to the world:

Cheap SE output transformers

There was also a thread where the 6AV5's were tested and abused:

Anyone know anything about a 6AV5GA?

This thread is about what happened when the two meet:

The Edcor meets the 6AV5

[Geek]

Hi Tubelab,

Originally posted by tubelab.com
No data came with the transformers. If you make amps like I do, you don't pay too much attention to manufacturer data. Use it for a starting point, then measure everything yourself. It would be nice to know the inductance of the primary, since my inductance bridge is dead. Measuring LF response of (-3db) 22 Hz at 5 watts says that it is good enough though.

I measured the L at 8H on the XSE15-8-5K with my DMM. I know my meter is chinsey on larger inductances, so I'd say it's more like 10H.

I always go by my own measurements. Like any other component, the only way to test if anything is suitable in *your* circuit, is actually in your circuit

[wrenchone]

This little project has gotten me thinking. 300Bs are nice because of their 40W plate dissipation, among other things. However, they are much too much the flavor of the moment, so their price is not nice at all. With that in mind, I nailed down a quad of Reflector 6550s on EBay, which have a similar plate dissipation and will probably sound pretty keen in a triode-strapped single-ended application. It's getting to be an addiction....

[tubelab.com]

I got talked into the 300B thing a few years ago by a customer who just had to have a 300B amp. I have built about 5 300B amps since then. I have never heard any of the high priced 300B's, and I don't want to. Like you said, it is an addiction.

I am currently using Chinese Shuguangs, which are under $50 each. I have bought about a dozen of these with no failures, and they sound good.

I had bad luck with Sovtek 300B's, 50% failure rate, and New Sensor would not replace any of them. The ones that didn't die in the first 6 months are still working 3 years later and sound good though. They are in my 300B push pull amp. I have yet to find ANY other amp that flat out rocks the way that one does.

I also have a old quad of Sovtek 6550 WE's these also rock. I sold the amp that they were in, but kept the tubes.

[rcavictim]

Originally posted by tubelab.com
I got talked into the 300B thing a few years ago by a customer who just had to have a 300B amp. I have built about 5 300B amps since then. I have never heard any of the high priced 300B's, and I don't want to. Like you said, it is an addiction.

I am currently using Chinese Shuguangs, which are under $50 each. I have bought about a dozen of these with no failures, and they sound good.

I had bad luck with Sovtek 300B's, 50% failure rate,

I have less total 300B experience than you but my limited experience with the Shuguang 300B carbon plate has been failure free with good sound. My experience with ElectroHARMonix gold grid (aren't these made by Sovtek?) has been 66.6% failure rate as delivered, forget even getting a few minutes from a new matched pair.

[wrenchone]

At any rate, I'll be tying the 6CD6GAs first, screen driven, as I have the iron and tons of tubes. If I hanker for more single-ended power after that experiment, the triode-strapped 6550 would be next, maybe with some pricier iron than the Hammond 125 budget series. I'm rather disturbed about the failure rate on some of the 300Bs as mentioned - that's a pretty expensive fuse/paperweight.

[tubelab.com]

Yes, I was really pi**ed off at New Sensor when 5 tubes died after the 90 day warantee was up. The best one lived 6 months. They basically said tough s***. Try our new Electro Harmonix 300B, it has an improved filament. This was right after they said that there was nothing wrong with the filaments in the Sovtek tubes.

The amp went into the closet and I forgot about it. A year later I got some used Sovtek 300B's at a hamfest for cheap, and popped them into the amp. They have been playing happily ever since (about 3 or 4 years). This tells me that the problem must be lot related, some are good and some are not so good! Yes they are real expensive fuses and they blow far too often. Most of my complete amplifiers cost less than I paid for these tubes.

I built a 45 amp because I got some cheap ($5 each) on Ebay before they became ultra trendy. I had a customer who liked the amp but wanted more power, so I put in 2A3's. He wanted more power, so I put in 300B's, the good Sovteks borrowed from my P-P amp. He liked it, so I bought the Shuguangs. I have made several more of these amps, including one for me. It is the Lexan amp that is on my web page. That poor amp has been offered up to science many times. In fact I connected the 6CD6's into it with clip leads for the experiments earlier in this thread. It currently has 6AV5's in UL wired into it.

I have a screen driven 6AV5 P-P amp on a breadboard that makes over 80 watts without trying hard. I may try 6CD6's and other sweep tubes in it when I get time to play, but now the tubes are not the limiting factor. I am limited by the power supply (550 volts max) and the OPT.

[wrenchone]

I'm setting up to run some curves for a few 6CD6GAs in screen drive mode with the control grid grounded. I'll post curves when I get them. I got the test jig set up this afternoon with filament supply - now I need to throw together a variable HV supply that won't kill me.

On another note, an 807 or 1625 might be a nice candidate for screen drive. The plate dissipation is nice at 30W, and they'll put up with a lot of plate voltage. Filament requirements are much more modest as compared to the 6CD6GA. As I've said before, though, I'll try what I have first.

[tubelab.com]

I have plenty of both of those tubes. I will try them but it must wait until I get back from my trip.