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807 in the mini torii (Read 2632 times)
Kevin
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807 in the mini torii
05/03/12 at 03:23:08
 
The 807, like the 6BG6, is essentially a 6L6 with an anode cap. It was used as a transmitter tube in WW2, and by HAM enthusiasts for decades after the war. Once in a while you see custom builders using the tube in push pull or single ended amps. Also like the 6BG6, these tubes can be had quite cheap.

So I ordered some adapters and a pile of 807 as well as a pair of 5933 (the ruggedized military version of the 807). End result is that these tubes work very well in the Mini Torii. Big, lush and powerful presentation.

The 5933 brings a bit more detail and ambiance, but the original 807 is dirt cheap. I got a dozen in one lot, which worked out to be about $4 each; all 1940's and 50's American tubes by RCA, National Union, and Philco. Great stuff! The 5933 are Sylvania. The 5933 also has a much wider base, so keep that in mind if you want to try them in another amplifier (no issues with clearance in the Mini Torii).

So Mini Torii owners, you also have a single ended 807 or 5933 amplifier!

5933 pictured below:





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« Last Edit: 05/03/12 at 03:27:17 by Kevin »  

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Les Lammers
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Re: 807 in the mini torii
Reply #1 - 05/03/12 at 11:21:53
 
Cool. I picked up the Sylvania 1952 5933's, Radiotron Australia, Mullard and Japanese Channel Master 807's.

Are you using the MiniMax pre with the Mini?
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Fireblade
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Re: 807 in the mini torii
Reply #2 - 05/03/12 at 15:16:17
 
It's incredible the level of versatility on this amp!  One question:  Are these 807's and 5933's drawing the same current and voltage specs of the stock 6V6's?  If not, are there any possible reliability issues? Is there any strain on the rest of the circuit given these different specs?

Also, how difficult is it to set up the 'adapters'?

Somebody needs to start a 'preferred tube' ranking thread among Mini Torii tube rollers, soon   Smiley
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« Last Edit: 05/03/12 at 15:18:17 by Fireblade »  

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Kevin
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Re: 807 in the mini torii
Reply #3 - 05/03/12 at 19:18:55
 
The 807 is a 6L6 variant, not a 6V6. I bought the adapters on that auction site, but if you know what you are doing and have the parts it is likely fairly easy to make a set.

Yes, I am using the minimax pre with the mini torii. I tried it without of course, but prefer the sound with the preamp in the chain. I also like having one nice heavy volume knob.
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« Last Edit: 05/03/12 at 19:20:12 by Kevin »  

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Fireblade
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Re: 807 in the mini torii
Reply #4 - 05/03/12 at 20:18:46
 
I know these are 6L6 variants, not 6V6's.  This is precisely the core of my question.  The fact that you can adapt a tube into the amp does not necessarily means is going to work flawlessly without some adjustment.  It may or may not be necessary in this case, that's why I asked.
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Kevin
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Re: 807 in the mini torii
Reply #5 - 05/03/12 at 21:22:58
 
Oh I see. Well, I'm not an expert, or even close to one, but my understanding is that the 807 is identical to the 6L6 electrically, but has the plate terminal connection moved to the top to place it physically distant from the rest of the tube components, thereby preventing arc over and allowing the tube to handle a much higher plate voltage for transmitting purposes. If anyone reading has better info than that or a reason not to use the tube, please correct me.

The 6L6 is approved for the mini torii. Whether it is optimal or not is a question for Steve. I can say it sounds very good to me, and certainly better than any 6V6 I have tried in this amplifier. Your mileage may vary.

The low cost (after adapters of course) is another big attraction. 12 great tubes for less than the price of one mediocre pair is a good value to me.

The 350B certainly draws more current than the 6L6, and no problem with that tube it seems.
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Fireblade
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Re: 807 in the mini torii
Reply #6 - 05/04/12 at 00:10:52
 
Ok, thanks for the info.
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Les Lammers
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Re: 807 in the mini torii
Reply #7 - 05/04/12 at 18:13:37
 
FB,

My understanding of the 807 is the same as what Kevin wrote. Tubes are like spice. There is no right or wrong..just personal preference. I bought some 807's to try in the Mini but also have a 6L6 amp. If you want to try a 6L6 type I'd get a pair of the Valve Art 350B's for about $50 shipped and no adapter is needed.
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« Last Edit: 05/04/12 at 18:14:29 by Les Lammers »  
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Fireblade
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Re: 807 in the mini torii
Reply #8 - 05/04/12 at 19:11:25
 
Florida Boy,

Excuse my lack of experience.  I just thought there would be a tradeoff in terms of circuit dynamics when going for tubes that are at the limits of the original design.  In other words, the amp has been tunned for 6V6's, and even though it can accept related different families of tubes, sometimes these require different current ratings and such, which make me wonder what tradeoffs are involved.

Is it tube life span, or for example early aging of insulators and other components due to higher heat dissipation, or maybe reduced headroom given output transformers reaching their ceiling sooner with more current demanding tubes, etc.?

Something has to give in, since the original design is optimized/voiced around the 6V6 tube.  Although the transformers, for example, are designed with high redundancy, ceteris paribus their capacity limits would be reached sooner with more demanding tubes, at least in my view, with possible headroom being reduced before clipping, etc.

How do we know, for example, if the tiny specd coupling capacitors or some other components in the topology are comfortable and non vulnerable to still compatible yet extreme output tubes?

If I were to choose a set of alternate tubes, I would use the ones that best sounded in my system, but chosen from those closer in their specification and general behavior to the 6V6.  Or, conversely, learn what would be the logical adjustments in the circuit to optimize it for the different demands involved in tubes behaving more radically than the 6V6s in this particular circuit design.

What about rectifiers, input drivers, etc.?  Aren't some of these prone to react differently to some more demanding conditions?

These are all intuitive and logical questions I ask myself when considering tube rolling.  The ideal setup, again, should not be at the expense of some possible inadvertent tradeoff that may trigger possible failure scenarios or shorter lifespans from the gear.

I would just like to learn how to address these concerns.  And, yes, I've noted the Valvo 350 B as one of the good alternatives for the post break-in stage, but would feel much more comfortable understanding the expected effects these may pose to that circuit's behavior.
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