KT66 Amp - Summer Project Help Wanted

[Kinkless Tetrode 66]

I have some time and money to spare this summer, so I would like to build an amp head with 2x10 cabinet, I am still considering combo... I will be using two 10' Jensen Tornado speakers (fyi). I got a good deal on some Sovtek 5Y3's & GT KT66's; so I would like to use them... I would love to have a volume, gain, tone and reverb control (if, it possible to fit tank in head...?) The lower the weight, the better! Since, I travel quite a bit, does anyone know of a way to get both EU & US power to work without external transformer. Could anyone show me a circuit or pictures? Any input is appreciated! Please pardon my ignorance. Thanks.

[Phil_S]

Get a power transformer with dual primaries. Use a switch to select input voltage. Use an IEC power inlet for the power cord and then you can choose the correct cord for the country.

You may have to make some compromises. I imagine, just like the US, the voltage supply can vary +/- about 10% and this affects heater voltage more than anything else.

The weight will come from the transformers, which will not be small for KT66's. Once you put the amp chassis in a head box, expect it to weigh about 25 pounds (~12Kg) or more.

In terms of a circuit, you did not give us any idea what you like, how many watts, etc. If you want lighter weight, you might consider a single ended amp as you might be able to use smaller transformers. The reverb will add some weight, but not that much. Reverb is likely to increase the size of the chassis, meaning the head box will be heavier. Think about your priorities. These will affect your options. If size and weight are important factors, I'd give up the reverb.

[Kinkless Tetrode 66]

I think, I will stay with the reverb (it's an addiction). I would probably be looking at a push/pull KT66 design. My only concern, with the SE design is the volume for gigs (8-9 watts?). I think I am looking for a push/pull design. Basically a simplified blues breaker, with spring reverb, gain, volume and tone controls. Thanks for the prompt reply!

[Bob S]

Big Bottle Rocket Reverb !
Sound great with KT66's.
If you search the TW section there are some previous schematics / layouts.
Have Fun whatever you choose.

[martin manning]

KT66 will drop right into any EL34 p-p circuit with a bit more negative bias voltage.

[Firestorm]

Push-pull with KT66: probably have to give up on using the 5Y3s (unless you use two).

[stephenl]

8K primary OT, 390v Plates, 275v screens,220 - 250R shared cathode resistor = class A bliss with PP KT 66's - My favorite PA setup.

A 12AV7 with 82k plate, 680R cathode, and 12 to 15kohm tail makes a great sounding LTPPI in front of it.

[Phil_S]

I think, I will stay with the reverb (it's an addiction). I would probably be looking at a push/pull KT66 design. ... Basically a simplified blues breaker, with spring reverb, gain, volume and tone controls. Thanks for the prompt reply!

I think I'd lift the V/T from a standard Marshall 18W TMB, which has one V+TMB section and one V+T only section. Lift the V+T section. Pair that with the JTM45 power section, which is meant for a pair of KT66.

I don't know much about reverb. I think I'd just lift the design from a 40-50W Fender model that uses a pair of 6L6.

Then you can have a real Frankenamp that should be what you describe.

You might be left with an unused triode I don't really know. If that happens, maybe you can figure out how to stuff tremolo in there, too. There must be one with a single tube design.

[M Fowler]

Or just use the Marshall 50w transformer set like Mojotone does on their bass amp running KT66's. OT is 3k4 primary.

[jazbo8]

Forget the 5Y3, just use SS rectifier and check out Dr. Z's Route 66, it only has 4 tubes, no reverb though... which you can add easily by adding another tube and tank. For international voltage, get a power transformer with 110/220V windings, so you can switch the line input voltage.

[overtone]

Is that just a single tone control that you are after?

For mobility I actually find a head and cab more versatile. The weight is spread out and sometimes there is already a decent cab where you are headed to anyway.

Did you know that Ingo Georges in Schwarzwald has dual input / primaries on most, if not all of his power transformers? Those are serious pieces of iron without having to resort to "fat stack" extra weight.

As to wiring a dual input, usually for 110V input the two primary windings are connected in parallel but you need to follow the manufacturer's instructions. If the wrong leads are connected the fields cancel each other. For 230V usually the two coils are connected in series, but again check the schematics of the manufacturer.

There are short tanks from Accutronics.

+1 the big bottle rocket suggestion, but not with 5Y3. Lots of information and guidance on that topology ready to be searched for here. The addition of reverb has been covered too.