syn

Altec 436c 6bc8 sub.
« on: November 03, 2009, 08:09:08 AM »
Hi
  
     I'm looking to build 436c with what I have at hand, and I don't have any 6bc8 but do have 6BQ7A.Would that work as a a substitute for 6bc8? From the data sheets they look quit similar, but still I'm not sure... How about the value of R3 and R4 from the 436c schemo? Do I have to alter those values?Also I'm using 100uA meter, is 100r trimer in a place of R8 O.K.?
6BC8  6BQ7A
Thank you
« Last Edit: November 03, 2009, 08:19:43 AM by syn »


simonsez

Re: Altec 436c 6bc8 sub.
« Reply #1 on: November 03, 2009, 09:15:29 AM »
6BC8 is semi remote cut off tubes...
@simonklontz

Rob Flinn

Re: Altec 436c 6bc8 sub.
« Reply #2 on: November 03, 2009, 11:04:21 AM »
6BC8 is semi remote cut off tubes...

& is also quite cheap, & is the same as a 6bz8. 
regards Rob

syn

Re: Altec 436c 6bc8 sub.
« Reply #3 on: November 03, 2009, 11:20:13 AM »
& i'm not having any on me right now. ;D
so the question still is how to adopt 436 circuit to work with 6BQ7A?
on several threads there are hints that this tubes are "plug and play"
equivalents but no solid confirmation.
cheers

pyjaman

Re: Altec 436c 6bc8 sub.
« Reply #4 on: November 03, 2009, 07:34:47 PM »
I didn't do it, but I'd compare datasheets of both tubes, and then try to look how each one of them could behave in this configuration. Couldn't be so hard to get a rough idea looking at the Ia=f(Ua) curves.

Laurent.

edit: In fact, not so easy (for me, at least). Some bias point seem comparable,though, but it seems that it becomes more and more different as CV negatively grows, and tube cutoff seems to be reached much sooner... but let the smart guys answer better than that...
« Last Edit: November 03, 2009, 08:38:57 PM by pyjaman »

syn

Re: Altec 436c 6bc8 sub.
« Reply #5 on: November 04, 2009, 02:12:39 AM »
thank you  pyjaman, i'll have a closer look at it, very good point.

this is a quote from PRR ,from another thread:
"I note the plan says 6BC8 but you say 6BQ7. These two tubes are similar but not the same. The 6BC8 has more control range."

I'm not looking to build an ultimate vari-mu, just something that will work well, within it's limitations, whatever they'll turn out to be...
cheers
« Last Edit: November 04, 2009, 02:14:31 AM by syn »

V9977

Re: Altec 436c 6bc8 sub.
« Reply #6 on: November 04, 2009, 02:44:12 AM »
Have you considered geting one from ebay? With a key
component like this it would be worth it to get the original
especialy if you already have most of the other parts.
Here is a listing for a GE type tube with low price and worldwide
delivery:

http://cgi.ebay.com/6BC8-6BZ8-GENERAL-ELECTRIC-VACUUM-TUBE-EMISSIONS-100-98_W0QQitemZ110440460353QQcmdZViewItemQQptZVintage_Electronics_R2?hash=item19b6c3b041

 :)
CAUTION:  Equipment is alive

syn

Re: Altec 436c 6bc8 sub.
« Reply #7 on: November 04, 2009, 03:17:37 AM »
V9977 thank you for good intentions.
best

simonsez

Re: Altec 436c 6bc8 sub.
« Reply #8 on: November 04, 2009, 12:29:23 PM »


I'm not looking to build an ultimate vari-mu, just something that will work well, within it's limitations, whatever they'll turn out to be...
cheers
[/quote]

Just plug the tube, i think it will work.
@simonklontz

syn

Re: Altec 436c 6bc8 sub.
« Reply #9 on: November 04, 2009, 12:56:59 PM »
simonsez, yes i did and it works. i have no 6bc8 to compare it to, but it does what is suppose to do. couldn't get rid off thump thou (inserted 200r trimmer between cathodes but not much change).is it possible to loose thump entirely or some amount of it will be present at all times? i might be getting interstage transformers...
i'll be playing with this for some time and then decide what will i actually build...BTW i just saw your  6BA6  and it looks fantastic!
cheers


simonsez

Re: Altec 436c 6bc8 sub.
« Reply #10 on: November 04, 2009, 03:46:43 PM »
Yes, adding interstage transformer help me deal with thump (Actually i use power tx ;D..don't tell CJ :-X, or you can try different tube, or try adding balance trimpot on the plate ala UA175. but of course it's not Altec anymore...
@simonklontz

syn

Re: Altec 436c 6bc8 sub.
« Reply #11 on: November 05, 2009, 04:32:16 AM »
What ratio (i want say a word to CJ)? Any other specs? Do tell more, please.
« Last Edit: November 05, 2009, 06:31:28 AM by syn »

simonsez

Re: Altec 436c 6bc8 sub.
« Reply #12 on: November 05, 2009, 05:51:27 AM »
P :220V  S :48V, but i think your post amp is not sufficient to make up the gain loss.
@simonklontz

syn

Re: Altec 436c 6bc8 sub. New
« Reply #13 on: November 05, 2009, 06:45:59 AM »
I think that 1k trimm at the UA175 schemo(R13-1k) from the anodes is to help transformer balance out the DC? No?
« Last Edit: April 27, 2011, 04:31:24 PM by syn »

Re: Altec 436c 6bc8 sub.
« Reply #14 on: November 07, 2009, 03:41:03 PM »
Russian 6n5p will replace the 6bc8. It draws more heater current but sound much quieter and transparent. I put them in my altecs when I want a less "compressed" sound . Theres also an output tube with the same number.
Dont get those by accident.
« Last Edit: November 07, 2009, 03:44:06 PM by lewilson »

syn

Re: Altec 436c 6bc8 sub.
« Reply #15 on: November 07, 2009, 04:56:33 PM »
lewilson
   
              i just have some 6n5p on order. so how do i distinguish which are for the input and which are for the output? i know about 6n3p (output type)...
thank you

pyjaman

Re: Altec 436c 6bc8 sub.
« Reply #16 on: November 15, 2009, 06:28:40 PM »
you can't get wrong. The "output" (power) 6n5p is a chinese big octal tube. The russian  (6"H"5Pi cyrillic) tube is a small noval dual triode (like is 6bc8).

Laurent.

syn

Re: Altec 436c 6bc8 sub.
« Reply #17 on: November 16, 2009, 05:27:32 AM »
Laurent
            thank you.

skal1

Re: Altec 436c 6bc8 sub.
« Reply #18 on: November 16, 2009, 04:15:13 PM »
hi

can some one explain why  their are 2 voltage's shown at the 6bc8 , 65, and the 285.

i have always wonder what these voltages mean, what is it telling you ?



skal1

syn

Re: Altec 436c 6bc8 sub.
« Reply #19 on: November 16, 2009, 04:54:36 PM »
voltages in "ellipse" are voltages under 20dB of compression. others are with no compression applied.


 

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