Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: thomash on March 23, 2018, 08:17:33 am

Title: 1650F wiring for 8 and 16 ohm output
Post by: thomash on March 23, 2018, 08:17:33 am

Hi all!

I have a small question; I am a relative newbie to building tube-amps and so far have produced a 5F1 clone in a wine-crate about 2 years ago (attached a photo for your enjoyment). Now I am working on building Sluckey's AC15. The question is about the AC15 build and specifically wiring the secondaries of the output transformer.

I understand these three wiring schemes (http://"http://www.hammondmfg.com/1608.htm") for 4, 8 and 16-ohm independently, but how would I go on to wire it to two jacks (8 and 16-ohm) without a switch of some sort?

In Sluckey's amp-build page, specifically this photo, http://sluckeyamps.com/VAC15/big_guts.jpg (http://sluckeyamps.com/VAC15/big_guts.jpg) it looks to me as it is wired for 4 and 8-ohm.. But I am not sure. I tried searching this forum and the internet, but I think I am not using the right terms to get some examples..

Thanks for your time :-)

And of course, once done, I will post some photos of the ac15 project! ;-)

Title: Re: 1650F wiring for 8 and 16 ohm output
Post by: sluckey on March 23, 2018, 08:38:15 am

Quote from: thomash on March 23, 2018, 08:17:33 am

I understand these three wiring schemes (http://www.hammondmfg.com/1608.htm) for 4, 8 and 16-ohm independently, but how would I go on to wire it to two jacks (8 and 16-ohm) without a switch of some sort?

Short answer, you can't.

The jumper is the same for 4 and 8 ohms so I chose to use 4 and 8 on my amp. Please note that this info is for the old style 1650F OT. There is a new 1650FA OT that has straightforward wiring that doesn't rely on jumping wires together. With the new 1650FA you can easily have 4, 8, and 16Ω output jacks if you want.

So, if you will be buying a new OT, get the newer one.

Title: Re: 1650F wiring for 8 and 16 ohm output
Post by: PRR on March 23, 2018, 07:09:06 pm

If you only have the "old" 1650F, I am 99% sure the mis-wire plan below will "work", just not at full Hi-Fi spec. 4 and 8 may not be "flat to 30KHz", and may have a part-dB extra loss. 16r should be pretty good. For guitar, there may be no difference at all.

Title: Re: 1650F wiring for 8 and 16 ohm output
Post by: thomash on March 24, 2018, 07:11:02 am

Thanks for confirming my suspicion.

I am stuck with the 1650F; I also saw the new ones and well, I wish I had one of those.

Currently, I have an old 16-ohm Wharfdale speaker which I plan on using. I will probably just wire one jack and eventually change the wiring to a more future-proof solution if I ever decide to change the speaker.

PRR's solution is something I don't yet feel ready for.. Putting in too much effort at the moment to willingly add a hacky solution (no offense meant here ;-) ).