Smallish "Jazz" amp build ideas.

[thomj513]

New member to this forum but not new to building tube audio products. I’m seeking input, suggestions, schematic ideas etc for building a smallish guitar amp for my personal use. A little background first. I started playing guitar in the mid 1960s, continued on through the 1970s and 1980s in cover bands, original prog/rock bands and “casual” solo guitar and duo gigs through the 1990s. During that time my day job was working for electronic parts distributors of one sort or another so I was able to get most of the parts I needed without any real problems. Most of the builds I did were for home audio, preamps and power amps of one sort or another. From 2000 to 2010 I had some health issues so I didn’t build much. Now, I’m thinking of building again. I’m looking for a simple single-ended amp voiced for a “jazz” guitar tone. No reverb, no tremolo, just straight ahead guitar amp. Thought about buying an old Polytone but there are issues with that make even though they sound great. Your thoughts etc would be appreciated. Thanks in advance, TJ.

[martin manning]

How big is smallish? 20W?

[thomj513]

5-10 watts. Thanks, TJ.

[Stevem]

Even for just playing at home and with the mellow kinda bottom heavy tone used in jazz, I think output stage wise you would want 15 watts of clean powr.

Now 15 watts then means building with a 6550, KT88 or KT90, and a 15 watt single ended OT will cost some bucks so be prepared to open the wallet wide!

[martin manning]

There is this discussion going on right now, with this -5W Dumble (ish) preamp with single ended EL84 power stage getting props. That basic formula, Dumble preamp and SE power stage might suit you. A 6L6 would make near 10W.

https://ampgarage.com/forum/viewtopic.p ... 66#p439766

[Colossal]

A KT66 running single-ended sounds fantastic, especially when paired with a Two Rock sized 1x12 with ported back (elliptical opening about 30-50% of the panel area) and loaded with an EV12ML. Plenty of volume and plenty of low end. This requires a SE output transformer with a lot of mass, about the size of a 30W push-pull OT, not a piddly Champ-sized Playskool toy that most commercial single-ended amps seem to get stuck with.

[10thTx]

Why the single ended approach? Is that to keep the wattage low?

If the reason is keeping lower watts, ................ how about a 6BM8 power section with LTPI for maybe 7-9 watts?

I'll toss out an idea for your consideration ................ I'm not suggesting that you "should" do this.

Use a Princeton non-reverb preamp with a 6BM8 power section. Only 7 watts.

I pretend to play jazz sorta and I use this amp "The HoSo56 Minimalist" for that and it does indeed have a relatively clean tone. https://soundclick.com/r/s8itqp
I used Edcor trannies for this amp. It's small in size similar to a Princeton Reverb perhaps.

The idea I am suggesting to consider would be even a cleaner tone that I think would be suitable for jazz. And the LTPI would give it less floor noise at idle in my expectations.

With respect, 10thtx

[Phil_S]

Jazz amp to me means lots of clean tone. What smallish means is an open question because 5W will seem to be about half as loud as 50W. Is SE really what you want or were you thinking it's a way to get to reduced power? A pair of EL84 PP with the right preamp and PI would be very nice for 15W-ish clean tone. You will save a pile of money on the OT in a PP amp vs what you'll need for a SE amp. BTW, 15W is louder than some people imagine.

[thomj513]

Thanks folks. You've given me some interesting ideas to further explore and think about. I appreciate your input. TJ.

[bepone]

47k for all preamp anodes, 820R-1K in cathodes