GARNET BTO

[TIMBO]

Hi guy's, Again, while searching the net for info an array of stuff is put in front of you and something grabs your attention.
I have squarked about how lucky you guys are when you tell of you finds and your fantastic builds out of other peoples trash 
No such luck here so a VINTAGE build would be the only way to acquire one even thought it won't be very VINTAGE. 
So, does any one have one ,played one, schems, mods, anything???
From what i can find (only bits and pieces) this is a rather interesting amp and quite legendary.
BTO :- Bachman Turner Overdrive or Big Time Operator ???

From what i can find i pieced together what i can and because some of the circuit is different to what i am use to i may need help to JOIN THE DOTS.
THIS IS WHAT I HAVE DONE :-
The PREAMP is from the LB260D schem (i'm thinking "LB" may stand for LEAD-BASS  )
The STINGER (FUZZ) is from the PRO BASS 190 circuit (6AN8 tube) although the LB260D has a similar tube (6JW8) that uses only the pentode half in the STINGER circuit and the triode half for the TREMOLO circuit, but i don't want the tremolo so i went for the PRO 190 stinger circuit.
PI is taken from the power amp section that looks to be a standard power amp used by garnet and being different to what i am use to and was said to be a major part of the BTO. 
In the schem (L260D)it has a transformer that looks to be part of the TREMOLO circuit OR is it (i left this on the drawing hoping that someone with more experience with this part would know if it could be deleted it and the PI could be connected to the screens resistors of the power tubes.
The standard POWER AMP (L260D) has four EL34s which i don't have but i have 6L6s (X2 which is more power than i need) so i thinking that some values around these tubes may need to be changed.
A PPIMV may also be needed.
Not sure what the CAPS/RESISTOR between plates is??
Not wanting the TREMOLO a one tube REVERB is added.
Forgot the FX loop (passive) so i will ASUME that it will go between the reverb and the PI.
A fixed bias only because the original had it but it was connected to part of the tremolo circuit ,so where would it connect.
I pinched another one of Darryls ideas for the PSU that he uses the power two EL34 (about 390V i think)  .
Again a 12v transformer for the heaters which i can get a 12SN7.
I can get the 6an8 and 6JW8 cheap but i already have some ECL84 and ECL85 which appear to be the same (triode/pentode) but i don't know what to look for when comparing between tubes from data sheets  and if there is a similar tube that has a 12v heater that would be even better.
The OT i have is a hammomd 1750F that i bought by mistake that has a 4000 ohm primary and a 2 ohm secondary so if connected to a 4 ohm speaker would that give me a 8000 ohm primary and would that be too much for a pair of 6L6s??
I know that if this was put together it may not sound like the ORIGINAL but thats as close i will get  Thanks

[The_Gaz]

Too lazy to read your whole post, but you should check out Garnet's amp building book, which has every Garnet schem in it and a bunch of other great info. Very cool amp.

[tubenit]

Here is a GIF version of the schematic Timbo drew. 

Timbo, you come up with some GREAT stuff!  Thanks for sharing it.

With respect, Tubenit

[tubenit]

Here are a couple of Garnet BTO schematics from the Hoffman Library of Schematics:


http://www.el34world.com/charts/Schematics/files/garnet/garnet_l260d_bto.pdf

http://www.el34world.com/charts/Schematics/files/garnet/garnet_pa260_bto_pa.pdf

With respect, Tubenit

[TubeGeek]

Timbo,

There a few guys around my area that are collecting Garnet's.  I see them in for servicing.

I have pics of a garnet reverb unit and recently a stinger came across my bench.  Pretty cool fuzz device!  I liked how you could have thick fuzz without crazy feedback, the circuit seemed to "gate" off when you stop playing.  I didn't disect the amp, just a quick repair and it was back to it's owner.

I can send you some pics if you think it may help out with your project.

[TIMBO]

Thanks Tubenit, Got the schems from Doug and the rest off the net. Any info would be great TubeGeek. The tubes are pretty cheep but i was hoping to get a similar tube (6AN8, 6jw8) that has a 12.6v heater ,any ideas.

[darryl]

...i was hoping to get a similar tube (6AN8, 6jw8) that has a 12.6v heater ,any ideas.

7059  I haven't tried them, but they seem to fit the description.

http://tubedata.milbert.com/sheets/049/7/7059.pdf

[TIMBO]

Hi guy's, Rather interesting amp this one,i started looking at how a layout would look and what type board/tagstrip build would work. So i look at a photo of the original build and the use of minimal tagstrips were used, then it dawn on me that there was 7 tubes used  so a closer look had four tubes across the front of the chassis. I assumed one the 6AN8 (stinger) two the 12AX7 (input) three 12AX7 (reverb, i'm putting that in other wise the tremolo) four 6SN7the PI and five and six the power tubes. What was the other tube, well it looks like it's the other tube in the input, Half 12AX7 at the input (one tube) and half 12AX7 (another tube)after the tone stack. 

Why the two tubes, stop cross talking. 

I found another garnet amp using the 6SN7 PI (more conventional way) can anyone give any fores and against the way i have drawn it to the split PI drawn in the original.
I have drawn the schem as what i found in Doug's library but it does not look right, i can't see how the two triodes of the PI are linked together  . Thanks

[sluckey]

Here's your missing link...

[TIMBO]

Thanks Sluckey , i thought it a bit strange that there was two caps in series. What type of PI would call this. Thanks

[DummyLoad]

1/2 6SN7 is grounded cathode gain stage. other 1/2 is concertina or call it a a split load PI if you prefer.

--DL

[TIMBO]

Thanks DL, Haven't used this type PI in a build.

[darryl]

Here's your missing link...

With the necessary missing link in place, there is now a .002 mfd capacitor from Pin 1 of the 6SN7 to ground. This would cause a significant treble cut, considering the high impedance in that part of circuit.

[sluckey]

Yep. I don't recall any screaming highs from BTO. Here's a Garnet schematic with that particular circuit...

http://www.el34world.com/charts/Schematics/files/garnet/garnet_b90l_l90l_lilrock.pdf

[darryl]

Maybe that cap is needed to keep the NFB loop stable. 

We await Timbo's build with keen anticipation.