Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on August 17, 2016, 01:17:55 am

Title: Which can be a substitute for the 7199 (only) pentode ?
Post by: kagliostro on August 17, 2016, 01:17:55 am

The substitutes for 7199 (triode + pentode) tube that are usually used (in audio) are the 6U8 and 6EA8

But which can be a substitute only for the pentode ? (noval - octal - 7pin ....)

7199 (Full datasheet >> http://www.mif.pg.gda.pl/homepages/frank/sheets/049/7/7199.pdf (http://www.mif.pg.gda.pl/homepages/frank/sheets/049/7/7199.pdf))

(http://www.mif.pg.gda.pl/homepages/frank/short/001/7/7199.gif)

6U8 (Full datasheet >> http://www.mif.pg.gda.pl/homepages/frank/sheets/082/e/ECF82.pdf (http://www.mif.pg.gda.pl/homepages/frank/sheets/082/e/ECF82.pdf))

(http://www.mif.pg.gda.pl/homepages/frank/short/002/6/6U8.gif)

6EA8 (Full datasheet >> http://www.mif.pg.gda.pl/homepages/frank/sheets/093/6/6EA8.pdf (http://www.mif.pg.gda.pl/homepages/frank/sheets/093/6/6EA8.pdf))

(http://www.mif.pg.gda.pl/homepages/frank/short/001/6/6EA8.gif)

Franco

Title: Re: Which can be a substitute for the 7199 (only) pentode ?
Post by: sluckey on August 17, 2016, 05:40:25 am

Weber used an EF86 and 12AU7 to replace 6AN8 or 7199 in their Sunn clone...

     http://www.tedweber.com/media/kits/6s100_schem.jpg (http://www.tedweber.com/media/kits/6s100_schem.jpg)

And 5879 is a sharp cutoff pentode that will probably work just fine also.

Title: Re: Which can be a substitute for the 7199 (only) pentode ?
Post by: kagliostro on August 17, 2016, 07:11:48 am

Many Thanks Steve

I see ... but isn't the 1mA/V of 5879 and the 1.85mA/V of the EF86 far from the 7mA/V of the 7199 ?

EF86 (Full datasheet >> http://www.mif.pg.gda.pl/homepages/frank/sheets/010/e/EF86.pdf (http://www.mif.pg.gda.pl/homepages/frank/sheets/010/e/EF86.pdf))

(http://www.mif.pg.gda.pl/homepages/frank/short/001/e/EF86.gif)

5879 (Full datasheet >> http://www.mif.pg.gda.pl/homepages/frank/sheets/079/5/5879.pdf (http://www.mif.pg.gda.pl/homepages/frank/sheets/079/5/5879.pdf))

(http://www.mif.pg.gda.pl/homepages/frank/short/001/5/5879.gif)

----

What about the 6AK5 or the EF85 ??

(the first I've seen used in tube mic and the second in some PA amp, may be Philips if I remember well)

6AK5 (Full datasheet >> http://www.mif.pg.gda.pl/homepages/frank/sheets/137/6/6AK5.pdf (http://www.mif.pg.gda.pl/homepages/frank/sheets/137/6/6AK5.pdf))

(http://www.mif.pg.gda.pl/homepages/frank/short/001/6/6AK5.gif)

EF85 (Full datasheet >> http://www.mif.pg.gda.pl/homepages/frank/sheets/010/e/EF85.pdf (http://www.mif.pg.gda.pl/homepages/frank/sheets/010/e/EF85.pdf))

(http://www.mif.pg.gda.pl/homepages/frank/short/001/e/EF85.gif)

Franco

Title: Re: Which can be a substitute for the 7199 (only) pentode ?
Post by: xm52 on August 17, 2016, 10:00:10 am

The 6GH8A is a good substitute for the 7199. It is relatively inexpensive which means that it is cost effective for you to not use the triode. Unfortunately it's not pin compatible. Fortunately, an adapter is available.




https://www.tubesandmore.com/search/node/7199 (https://www.tubesandmore.com/search/node/7199)

Title: Re: Which can be a substitute for the 7199 (only) pentode ?
Post by: kagliostro on August 17, 2016, 10:04:32 am

Thanks for the info

but I'm not looking to a complete substitute

only I would like to know a pentode which is close to the pentode inside the 7199

Franco

Title: Re: Which can be a substitute for the 7199 (only) pentode ?
Post by: xm52 on August 17, 2016, 04:00:35 pm

Franco, I can see that you want just the pentode half. My point was more that since the 7199 is a $54 tube and the 6GH8A is $6.25. You can afford to buy the 6GH8A and not use the triode.  :smiley:

Title: Re: Which can be a substitute for the 7199 (only) pentode ?
Post by: kagliostro on August 17, 2016, 05:05:39 pm

Ah, OK, now I understand what you want to say


Franco

Title: Re: Which can be a substitute for the 7199 (only) pentode ?
Post by: Paul1453 on August 17, 2016, 05:28:28 pm

I tend to look at these substitutions slightly differently.

The Data Sheets give me lots of specifications and applications for usage,
But then tends to leave me out in the cold on actual usage in an audio circuit.

What I am finding that seems to get me where I want to go is:

I set up on my BB the simplest most stripped down circuit for the tube I want to replace.
I look at the data sheets for potentially compatible pentodes, in this case.
Then I just give them a try. 
Adjusting parameters accordingly, and whichever way tends to give me the results that sound best to me.
Granted, I have a vast supply of obsolete unused tubes I purchased for less than $0.25 a piece.
So even if I burn up a few in my misled adventures, I feel the knowledge gained was worth more than the cost of my tube.
Surprisingly, our tubes will usually take an extreme amount of abuse and still not die off quickly.

If you don't already have a supply of potential substitutes,
I don't know if that is of any value to you, or not.   :dontknow:

Title: Re: Which can be a substitute for the 7199 (only) pentode ?
Post by: kagliostro on August 17, 2016, 05:44:33 pm

I've a little stock of tubes and as I go quite often to Ham Fest, each time I give a look if I can find something of interesting

also I've an Hungarian Radio Amateur friend who is my russian tube supplier

so I've general interest for substitution of expensive tube

in this case my interest was because of a preamp (of a Playmaster amp) that uses only the pentode of the 7199

and I'm not interested on the other part of that amp

Franco

Title: Re: Which can be a substitute for the 7199 (only) pentode ?
Post by: Paul1453 on August 17, 2016, 06:16:23 pm

I have used the 6AK5 in a simple circuit on my BB before.
I was just copying someone else's design, but it seemed to do the job.
I have a whole bag full of those, and also 6AU6s that you might investigate.

I didn't have many EF86s, but am currently working on a preamp design with that and a 6DJ8, which I also have a lot of.
I am sort of enjoying trying out my odd tubes to see what will work.
There may be quite a few reasonably cheap subs that would meet your needs.
Of course when we leave the beaten trail, we are on our own to find our path.
In the future I hope to discover uses for the bigger bags of not seen in guitar amp tubes I have in stock.   :l2:

Title: Re: Which can be a substitute for the 7199 (only) pentode ?
Post by: HotBluePlates on August 17, 2016, 07:17:38 pm

Quote from: kagliostro on August 17, 2016, 07:11:48 am

I see ... but isn't the 1mA/V of 5879 and the 1.85mA/V of the EF86 far from the 7mA/V of the 7199 ? ...

Gm is generally the figure of merit for pentodes. However, to make any meaningful comparison between them, the Gm numbers need to be taken at/near the same plate current.

Notice the 7199's Gm number is while the tube is passing 12.5mA, while the EF86 and 5879 Gm numbers are from when they're passing ~2-3mA.

All tubes exhibit higher Gm at a higher plate current. So you'll need a more complete data sheet, and probably some investigation of the curves to find Gm of each tube at the same operating point.

Title: Re: Which can be a substitute for the 7199 (only) pentode ?
Post by: PRR on August 17, 2016, 10:25:46 pm

> 7mA/V of the 7199 ?

At 12mA.

The sheet you link shows a 1.1mA condition, MUCH more likely for an audio amplifier, and 1,500 uMho (1.5mA/V).

Which seems much the same as "1mA/V of 5879 and the 1.85mA/V of the EF86".

Title: Re: Which can be a substitute for the 7199 (only) pentode ?
Post by: kagliostro on August 18, 2016, 12:57:48 am

Quote

> 7mA/V of the 7199 ? At 12mA.

The sheet you link shows a 1.1mA condition, MUCH more likely for an audio amplifier, and 1,500 uMho (1.5mA/V).

 :bump1:

Thanks PRR

I'm only an ignorant ass (http://www.electroyou.it/forum/images/smilies/icon_redface.gif)

Franco