The Burger King 5-6-7

[DummyLoad]

why burger king? well, all the tubes are 6BKsomething_or_another...

6BK8 - semi remote cut-off pentode for audio use - not very popular & seems to be uncommon - euro equiv. is EF83 - same pinning as 6267/EF86.
6BK7 - PI - as far as i can tell, nearly as common as dirt, as far as tubes go.
6BK6 - 1st stage & summing amp - 6AV6 variant w/ same pinning - seems to be fairly common.
6BK5 - output pentode - also seems to be fairly common - probably used mostly for outputs on TV sets (just a guess). filaments are current hungry - 6 volt versions are 1.2A/valve

U1 will dissipate ~~10W - will need a fairly hefty heat-sink.

just fooling around - have not built yet - have everything except the 6BK8/EF83 - buttery had all the other tubes in his stash. thanks buttery.  

it's just a 5E3 with a 'lil twist.

--ISO

 

[PRR]

> 6BK8 - semi remote cut-off pentode for audio use - not very popular & seems to be uncommon

I didn't know it had a US type-number.

It was specifically made for a tape recorder automatic level control.
http://www.pocnet.net/hobby/bastel/tubes/tips.html

It is a real waste to use it as a straight pentode.

Find one of the simpler vari-Mu limiters. Final stage plate winding feeds caps and diodes to make control voltage. Bring that around to the EF83 grid (must block DC from the jack). Use the specific Ra and Rg2 values from the sheet, with little or no cathode resistor. It's a limiter, and the unique feature is that it is relatively thumpless for a single-ended limiter.

6BK7 was a very popular TV tuner front-end. I have used it as push-pull headphone "power" amp.

6BK6 ... I don't know why it existed, 6AV6 does the same job.

6BK5 is probably part of the deal to screw Armstrong on his ratio-detector patent. Some of the strange things used to evade his patent incidentally had high output, but not enough to flog 6AQ5 etc. It seems to have topped the charts in 1954-1955 with a short-wave radio and five TV sets, monsters with 24" screen and 10" speaker.

[DummyLoad]

It is a real waste to use it as a straight pentode.

errr... too late for one anyway - 6 on the way.   

[DummyLoad]

was only able to procure 3 of the 6BK8...

...but they are lovely three.



i'll start strapping on the breadboard tomorrow. 

[PRR]

EF83 is really made to be used variable-gain.... otherwise the EF86 is the go-to tube.

Can't you use a vacuum-toob vari-Mu compressor? Guitar-quality: not much choice of ratio of rate, audible coloration, some thump. Not so many added parts.

[DummyLoad]

Can't you use a vacuum-toob vari-Mu compressor?

okey dokey - since it's on the BB, i'll give it a shot.    

are the diodes drawn correct? it seems like one should be reversed.

i'll scribble in updates of the PRR G-Vmu into the schematic i posted... just for clarification and to not foul things up - i usually do.

thanks much and happy new year!

--pete

edit: never mind... i'll build PRR G-Vmu stand alone and go to 6267 - you do know i'm going to try the EF83 in V2 anyway, right? 

[DummyLoad]

are the diodes drawn correct? it seems like one should be reversed.

never mind...  i see the reason for the polarity. 

[DummyLoad]

this amp is a lot of fun. with only thee controls it's pretty versatile. blend pentode and deluxe-like triode overdrive. sustain and feedback control are really nice, with a very harmonics rich overdrive. roll back on the guitar volume and twang away with kinda'-deluxe-like clean tones.

add a cross-line MV (a-la matchless) if you wish. i plan on experimenting with that on the BB shortly.

enjoy!

--ISO

 

[DummyLoad]

a likely future build on a PCB. i'll post the artwork when i have a working prototype.

PTs are Stancore 6378 and Stancore 6377.

fun little amp  - about 7-8WRMS output.

sluckey - remember we bounced back and fourth ideas of a all 7 pin tube amp?  how about something like this w/ 6AU6A, 6J6 PI, and 6AQ5/6005 P-P finals, DC fils on pre-amp - similar topo?

final schematic attached - now on to a 4 x 6V6 princeton reverb for a friend and another thread as i have some questions...