Got 2 6BA6s want 2 experiment with Vari Mu hybrid

[gary o]

Got matched pait 6BA6Ws { matched as triodes}.....As an experiment I want to copy the front end circuit from a vari mu limiter that uses the 6386
I have a DIY BA6A thats working great & 6SK7s for the gain control job..I plan to graft in the new 6BA6s to the front end of the BA6 just to hear the difference in charactor.

Im gonna copy like I said a vari mu circuit of another unit.....was thinking that the Collins 26U looks to be good candidate ?...My friend I bought the tubes from matched picked a matched as triode pair for & said use cathode resistor 150 to 180 ohms

would like to hear any thoughts about my little plan.

Thanks for reading

 

[solder_city]

im not really understanding what youre trying to acocmplish. but if youre interested in how the 6ba6 is going to do in the ba6a circuit, why not just use the ba6a circuit instead of something else?

 

[gary o]

The BA6a sounds fantastic as is ....just want to here the limiting characyoristics of the 6BA6s instead of the 6SK7s within the BA6 circuit is poss, the BA6 has great sound just as amp havent got parts for full 26U anyway

Didnt the 6386s come along later the 6SK7s...RCA made later than BA6 limiters using 6386s theres so much talk about the 6386 I thought id try to see what the fuss is about, although I know the 6BA6s arent exact as 1 X 6386 thought might be fun & maybe i can learn a little more

Thanks

 

[gary o]

Its up & running.....fried a resistor in the BA6A tho replaced it with higher wattage now it runs warm

had control voltage popping as soon as it limited ...but trimmed the cathode pot & that went away

I have variable attack & release setting not on original BA as well as orig BA time constants seems to work slightly better in variable mode some times there small thump on the attack ..seems like the ba6 time const is too fast for it

experimented with different resistors feeding the interstage tran...seems to work smoother with the resistors on the inter in the BA6 circuit rather than the 6386 type circuit

I spose its coz its different transformer

the sound was more squashy ..less toppy the BA6 standard...the BA6 in orig design does have a special sound I love, it has a kinda extra silk sound above the rest of the sound compared to my DIY LA2A had it has that & the BA with this modd sounds more like the LA2A

I then swapped the grids around the other way....does that change the Phase ?? that gives it more of that top sound, still not as nice as orig BA tho

Not really expecting too much as i no these things werent designed to be together just thought it would be interesting..

Im about to mess with the cathode resistors to hear what that does .....thanks

 

[gary o]

A useable sound can be had from the 6BAas in the BA6 ha sounds cool a sound that is different to the origig BA6.

One bad thing that happens tho is on vocals the SSSSSsss sounds sound BAD...Im wondering why this is.

Been looking at all the vai mu schematics I have & I notice that s lot of the 6386 circuits have cap & res across the grids.....
Is this called a Zobel network ?
What does it do ?
Is that why I have horrible SSSsss sounds....coz I have no RC on grids
Why dont other circuits have RC on grids.. Ba6 has none

On the anodes of 6386, or in my case the 2 6BA6 triodes theres either or both a interstage tran pair of resistors...

Heres what I think I know the resistors or two input windings are a voltage divider to feed the anodes ( usually two 10K (for 6386) res to split power from 150V voltage reg, would give each anode 75 volts)

I also notice power fed thru the inter tran CT as in BA6A is this better ?
Spose need differ tran here ? ....more expense

The BA6A has power thru CT & resitors accross each winding...parrallell resistors would lower resistace...I read these were added later to the BA

The resistance of my interstage windings measures just 360 & 337 Ohms .....Seems low looking at resistors usually on 6386 anodes there usually 10K...Is this because its what the 6SK7s would usually want ??
Cant find any other limiters that use 6SK7s...

Do I need to calculate two resistors to go across the anodes & inter windings that add up to 10K ?

Im gonna try some RC networks across my grids to hear what they do & also mess with the anode resistances

Thanks for reading sorry some of the questions may seem silly to you Ive not been into electronics for that long & have jumped straight into making stuff & finding out how it works later....Cheers Gary O.