Champ circuit with KT88 tube

[Jackstraw89]

Hey All

I’m wondering what the viability of designing a fender champ circuit with a KT88 tube for extra headroom would be

Anyone think this is a good idea?

[xtian]

Meh. Are you a big fan of single-ended amps? I'm not. The OT is larger and heavier than P-P, and I find I have to add extra filtering (CLC) to stop the hum.

[drew]

Type “beast Champ” into the search box.

[Stevem]

There are 4 things you need for this build if you already have a KT88.

1) Hammond 269BX power transformer.

2) Hommomd 125GSE output transformer.

3) 10 watt wire wound 560 ohm or so output tube cathode resistor.

4) new output tube cathode bypass cap up rated to 50 volts.

[Colossal]

Eagle Supre
https://ampgarage.com/forum/viewtopic.php?f=6&t=14349

[Dr Tony Balls]

I've done it once upon a time. These two Weber designs are based off the Princeton, but same difference. Simple SE amp, bigger power section:

https://tedweber.com/5f2h-c-kt/
https://tedweber.com/lauren-c-kt/

I started with the "Lauren" design and worked from there:

[roberto]

1) Hammond 269BX power transformer.

That trafo is weak both for B+ voltage and heater current.
300 CT means 150-0-150V, that will give you around 200V B+ with that configuration, if you consider also the drop across the cathode resistor, the KT88 will starve.
On top of that, you have only 86 mA, that's nothing for a KT88.
KT88 heater current is 1.6 A plus 0.3 A for the 12ax7, you are right on the edge, better to have a safety margin on that because of tolerances.

You need to change the PSU completely.

[echuta13]

I built a 5f2a up with one and it turned out well. I used a Doberman AX84 SE OT built by Heyboer.
You can still get them here: https://reverb.com/item/37408661-ax84-h ... 6-kt88-etc

[Littlewyan]

I've often wondered about building a Single Ended amp. I have a spare Power Transformer in the cupboard that's just good enough for a single ended EL34 kicking out 10W, but then I think about how I can probably get a better tone and 18W out of EL84 Push Pull with the same PT. Are you on the same fence?

[thetragichero]

I've got a little single ended vibrochamp-type thing i built to use the sweet looking 6l6g i pulled (3) out of some old test equipment and it's my most played/recorded amp. power transformer is from a thomas organ (2xel84, although their iron looked puny compared to what Hammond used) with a big clc filter.... use it for referring but really heavy stuff (although boosted it can get a decent hair metal rhythm tone). i always joked at the champ but I'm a big fan of single ended amps now

[xtian]

Here's my SE "desktop" amp, where I use a CLC filter, and cascaded gain stages. Came out good.

https://ampgarage.com/forum/viewtopic.php?t=33171