200 Watt 6550 Power Transformer(s)

[chasbenson]

Hey guys,
I'm trying to figure out the most economical way to build a 200 watt 4x6550/kt88 bass amplifier using existing transformers. I don't want to buy the SVT clones. I like Hammond. I'm looking for 700+ volts on the plates, around 350-400 for screens, and I can invent the bias tap using the V4b method off of the high voltage windings. I'm hoping not to use another filament transformer like an SVT.
Any ideas? Thanks!

[chasbenson]

I'm sure SOMEBODY has an idea...?

[loudthud]

Weber sells a couple of transformers, but they are saying 300 watts. Link: Weber Transformers and Chokes Order Form

[diagrammatiks]

I would not tap bias off the hv supply for tubes you are going to run at 700 plates.

There really is no budget way to do the project if you want it to be stable.

Are you trying to build something like an SVT? You should plan out how you are going to run and bias your drivers as well.

look over ken's information for his big ass amp.

The Big Ass Guitar Amplifier | ken-gilbert.com

[chasbenson]

I would not tap bias off the hv supply for tubes you are going to run at 700 plates.

There really is no budget way to do the project if you want it to be stable.

Are you trying to build something like an SVT? You should plan out how you are going to run and bias your drivers as well.

look over ken's information for his big ass amp.

The Big Ass Guitar Amplifier | ken-gilbert.com

Why shouldn't I tap the bias off the hv supply? I know this is not going to be cheap, but the cheapest alternative I have right now is to use an SVT power transformer at a little less then 300 bucks that is also quite heavy....for an amp 2/3 the power!
In terms of drivers, I was going to use a 12at7 ltp phase inverter and add a current buffer only if I need it...keep the tube count down. I've seen 6x6550 300 watt amps done with such a driver that put out the full wattage...in style! I think el84s drivers are cool but a little much for a minimalist design. The high voltage for the preamp/drivers I plan on getting anywhere I can post plate or screen...class A constant current draw makes that easy, and I don't mind the preamp headroom shrinking if I drive the power section hard....compression in a bass amp is a good thing in my opinion.

[chasbenson]

That's not a bad option! I didn't know they had started carrying 300 watt transformers. Still want to get the weight down though....Thanks!

Weber sells a couple of transformers, but they are saying 300 watts. Link: Weber Transformers and Chokes Order Form

[Steve Conner]

Antek may well have a suitable toroidal PT for the job. Toroidal OTs aren't so hot, the low weight is the only good thing about them IMO.

[loudthud]

That's not a bad option! I didn't know they had started carrying 300 watt transformers. Still want to get the weight down though....Thanks!

Take a look at the circuit of the kit they sell with those transformers. 6x6550 transformer driven by an EL34. They use the OT at 8, 4 and 2 ohms instead of 16, 8 and 4 like the data sheet says. They also play around with the taps on the PT to get different voltages for different output tubes.

[Tage]

I am in the process of this type of build right now, I used a 430V 400va antek power transformer and the weber 300 watt OT, it has a ~2k primary impedance wich works well for this amp. I would not fear the weight, but I understand. I'm using mosfet current drivers and feeding the bias voltage through them, this set up is supplied by an additional isolation, 120V transformer.

I think you may want to consider looking over the schematics of the Orange AD200, they are a couple posts down. ALso the traynor YBA 200 for some ideas on voltages.

Orange AD200B Mk II Bass Amp

[Gtr_tech]

How 'bout this?
Servicing a Dirty Big, Dirty Old Amplifier

Amp? Audio wrecking ball? Weapon of mass (speaker) destruction?

[Tage]

That thing is nuts but I'm pretty sure outside the scope of the OP ideas/goals

[Gtr_tech]

Right....just funnin' around....

[Tage]

Well maybe that will be the next project down the road, 10-12 kt88's! and a few OT

[kg]

do you still need advice on this? what's your design looking like right now?

[imaradiostar]

How about some of these?

British Audio Service, Inc. */*Trace Elliot*Transformers

jamie

[GregS]

If you can live with 160W the Hammond PT278CX and OT1650T transformer set will do the job. The Traynor Custom Special is based on these transformers so you can refer to that if you're interested. One thing to note is that the heater winding is only rated for 6A so 4 x 6550/KT88 and a couple of pre-amp tubes will draw around 7+ A. The transformer can handle 25% above the rating continuously but you might want to keep this in mind if you're planning to use a lot of pre-amp tubes.

[imaradiostar]

Heyboer should be able to make a set that is more or less identical to the Hiwatt/Reeves or Orange design for similar money to Hammond. You will probably find this is an easier way to hit your voltage and power goals.

jamie