OTL, continued...

[fdegrove]

Hi,

column 3 is clearly heater voltage but if column 4 is heater current there are some errors, for instance for 6C33C.

Yeah...I was over that too.

That table looks a little like a leaf out the "Electronic Universal Vademecum".
I'll put it under the pillow tonight...see if that trick still works...

Cheers,

[jlsem]

Regarding that super 6C47C...Is this for real??? My goodness, this seems yet another of those military secret tubes no one has ever seen.

These are very powerful pass tubes for regulated power supplies. There exist similar American types (Tung-Sol 7XXX; can't recall exact number) that are essentially three 6336A in parallel. They are good for about 1.25A at 100 volts. Transconductance figures for these types are tremendous, upwards of 120 mS. Plate resistances are therefore very low, approx. 35 ohms. These figures are off the top of my head; there may be data sheets on Frank Phillipse's page.

John

[arteitle]

Originally posted by jlsem
These are very powerful pass tubes for regulated power supplies. There exist similar American types (Tung-Sol 7XXX; can't recall exact number) that are essentially three 6336A in parallel. ...

Here are links to two such tubes' datasheets at Frank's Electron Tube Pages:

7241
7242

The 7242 is rated for a max plate current of 900 mA; the 7241 is rated for 1.2 A. 7241 has transconductance of 40 mS, 7242's is 111 mS. Both have heater currents of 7.5 A at 6.3 V! Toasty.

[thoriated]

Hi -

With a quick look, I didn't see any tung sol entry under 7*** or the 6c47c at the frank philipse site. If anybody finds specs for these and who stocks 'em, I might be willing to go in on an order

Btw, some news on my dc coupled hybrid HT amp front. I've just prototyped an interesting input and driver circuit using a 6K11. It's basically just the two hi-u sections (12ax7 spec) as a long tailed differential amp driving the medium u section as a follower through a mild resistive level shifter (From about 100vdc to ground). The supplies are +/- 200vdc with a -600vdc supply for the level shifter divider. With this arrangement, I've got it sitting on a breadboard (no mosfet output stage hooked up yet) with unity dc gain and about 27db ac gain and the dc offset has stayed within 10mV of ground for the last hour after initial nulling with no initial sign of dc offset accumulating when an ac signal is applied to the input.

One potentially nice feature of this topology is that all the cathodes are near dc ground potential. Right now, I'm doing an indirect offset nulling. The high-u section driving the output follower has a much higher value plate resistor than the other section, thus the grid bias offsets depend on the overall current flowing through both sections. By trimming this current out by adjusting the long tailed resistor value, the bias offset can be neutralized without injecting dc signals into either input grid except for the input bias and feedback loop of course.

This might be very interesting sonically since the only gain stage is effectively the input diff amp. Basically, with a 26db closed loop gain, there would only be around 10db of feedback, but it's fairly simple to rig up a positive feedback internal loop which should be effective at helping to correct any mosfet output stage nonlinearities. This circuit should be easy to make unconditionally stable into a speaker load once the mosfets are connected with such a low available open loop gain while not rolling off the open loop response much below 20 khz. Plus this circuit seems capable of swinging to the rails of a +/- 56 vdc output stage supply right from the diff amp output. It looks like the medium mu stage should be good to go with a quiescent bias of up to 10mA to drive mosfets, although I'm running about 6.5 at the moment.

A dc coupled hybrid amp with only one 12ax7 type voltage gain stage? It sounds intriguing to me. Any opinions or observations from others about this?

[tubetvr]

Hi,

(It is not only max current in datashet that is important)

Even the 7242 can not do wonders, to pass 1A at 0V on the grid the anode voltage need to be ~90V, this is not so impressive for OTL use.

The reason is that although Gm is very high u is high also giving relatively high Ri, (Ri=u/Gm).

I am very interested in the 6C47 data to know if that has similar data to the 7242 or if it is better.

Compare the 6C33C that has low u and lower Ri then 7242 and can pass 1A at ~65V and ~1.45A at 90V and is therefore a better choice for OTL then 7242.

The perfect tube for OTL should have very high GM and as low u as possible with a big nice cathode with high heater power.

Regards Hans

[fdegrove]

Hi,

If anybody finds specs for these and who stocks 'em, I might be willing to go in on an order

The datasheets I may be able to find, the tubes themselves are quite a different story.

I've done enquiries with dealers many years ago, they never had a single one in stock.
With the 6C33-C hitting the market in the early nineties, even much sooner in Japan, I just stopped looking.

Last night I looked in the "Electronic Universal Vademecum", no mention of the 6C47-C. The biggest one being the 6C33-C.

Thoriated,

Good idea to use a compactron, these are often overlooked types.

Cheers,

[Tyimo]

Hi!
I attache a better picture about the data page. Here you can see what each column means.
I started to looking for infos about this "magic tube", but I need ca.1-2 weeks to get answers from Ukraine where I have some connections. I have a "goldmine" in Hungary where I can get 815-250, AD1, 6080, 6H13C, 6H5C etc. and my "miner" will also asking for the 6C47C in Hungary.
Could somebody tell me where can I (or We) find the full article of the Camorani OTL??? It is looking so nice... :-)
Greets
Tyimo

[fdegrove]

Hi,

The Camorani circuit is partially published here:

CAMORANI OTL

Cheers,

[markanica]

Hi
I noticed the quest for data and couldn't resist to google up this one:

http://www.russiantubes.com/prop.php?t=12&p=338

cheers

Mark

[Tyimo]

Hi!
I found the Camorani amp's parts list, but I am still interested for the whole article!
What could be lovest operational voltage for this amp?
Mark! Good site, thanks!
Greets:
Tyimo