Transformers for 4-KT88 Bass Amp

[Zozobra]

I'll add another +1 to using the Antek toroidal power transformers. They are incredibly cheap compared to EI transformers of equivalent specification.
I have one in a 2xKT88 build and I can't fault it.

I'd look at the edcor stuff if you want an off the shelf OT. They're priced well and offer many primary options and feature UL taps as standard. They'd be my go to supplier if I was in the US. They're rated for full 20 to 20khz bandwidth at 100W so you could push them beyond that if the bandwidth isn't too important to you. If you'd rather not do than then think about ordering something custom from Heyboer who apparently are quite reasonable. Ultimately draw your loadlines and make the call based on that.

[big_teee]

I'll add another +1 to using the Antek toroidal power transformers. They are incredibly cheap compared to EI transformers of equivalent specification.
I have one in a 2xKT88 build and I can't fault it.

I'd look at the edcor stuff if you want an off the shelf OT. They're priced well and offer many primary options and feature UL taps as standard. They'd be my go to supplier if I was in the US. They're rated for full 20 to 20khz bandwidth at 100W so you could push them beyond that if the bandwidth isn't too important to you. If you'd rather not do than then think about ordering something custom from Heyboer who apparently are quite reasonable. Ultimately draw your loadlines and make the call based on that.

Which Antek PT is suitable for this application?
Edcor does not make a PT with more than 6A of 6v heater secondary.
I looked into Edcor, but ruled them out because of the 6V limitations.
T

[GregS]

I used 4x6550 with the Hammond 1650T and 278CX. It does 150W. (Note the 278CX only has a 6A heater winding.)

I've also built amps using this same transformer compliment and 4 x 6550's which are the amps I currently use. With the bias at roughly 50 mA per tube the B+ is at around 565V. I measured 157W RMS into an 8 Ohm load and 162W RMS into 4 Ohms on my scope. The 1650T is rated at 120W down to 20 Hz. According to my scope measurements I'm still getting full output power (160W) at 40 Hz which is at the low E of a 4 string bass.

The heater current in my amps I measured at 7.2A which is above the 6A rating. Apparently, the transformer can safely handle 25% over the rating (7.5A)continuously without a problem. One of my amps has been in regular use for a year and a half now and the other about a month and a half and I haven't had any problems with this.

Greg

[bb5000]

Heyboer will make Hiwatt DR201 replacement transformers, I got my DR201 transformers from TubeAmpDoctor (6 weeks build + delivery time). Using the Hiwatt powersupply design, you
will get ~700 V plate and 400 V screen/preamp voltage, which works for EL34's or KT88's (the plate voltage is a bit too high for the 6550's). I use 6xEL34 or 4xKT88 in the DR201.
Weber had transformers for the AB200 kit (which is now unavailable), those transformers were more like Ampeg SVT CL transformers. I run the AB200 now with a dual-rail powersupply,
610 V plate and 390 V screen/preamp and 6x6550's.

[Zozobra]

Which Antek PT is suitable for this application?
Edcor does not make a PT with more than 6A of 6v heater secondary.
I looked into Edcor, but ruled them out because of the 6V limitations.
T

The AS-4T360 has 2x0-360VAC secondaries at 0.55A a piece which will be good for ~500VDC (if not more) as you aren't going to touch the sides of its current capacity. Additionally it has 2x0-6.3VAC at 4A each which should see you fine. Not bad for $57!
If you want higher B+ then look at the AS-4T400 (2x0-400VAD @ 0.5A, 2x0-6.3VAC @ 4A). Do bear in mind that there is no CT or bias winding. I used a capacitor coupled bias supply for my amp with an elevated artificial heater CT.

I was looking at Edcor here for their output transformers rather then their power transformers, which do seem a little skimpy.