6AQ5 TUBE AMP HOW TO
6AQ5 TUBE AMP SERIES

It has a certain “industrial” look to it, but it works very well.

I used a timed relay that was in my stock. Let me just say that I want to protect my NOS tubes as much as possible! If you use diodes for your power supply and you want the time delay, just use the octal (V1) socket for a delay relay #T-6C45-DR from AES. Much discussion has taken place about the benefits of the timed delay of B+, so I won’t go into it again here. I used the 5V4 type of rectifier tube for the B+ in the amp because it was in my stock, will handle the load, and offers the time delay that I think is necessary, which keeps the high voltage from hitting the plates of the tubes before the cathodes warm up. Just remember to use the correct type of input, a choke-capacitor input, so that, when used with the listed power transformer, your B+ won’t be too high.įigure 1B: DC blocking option if using push-pull transformers (Omit if using Hammond #125CSE.) I built two versions of the amp and I used tube rectification for the power supply in one and diodes in the other. Also, the wiring hookup for them is very easy.

6AQ5 TUBE AMP SERIES

Funny how the ears and the meters don’t always agree, huh? You may use any output transformer that has the required load for the 6BQ5s, but the Hammond #125 series is a good and inexpensive choice to consider. I could not detect much of a rolloff in the low end while listening to music, which, for me, is where it counts. I didn’t use it because, as usual, the engineers at Hammond are a bit conservative with their ratings, much as they were with the #125CSE transformers that I used in my “Mini Single-Ended Amp” project (aX April ’04).

6AQ5 TUBE AMP HOW TO

Later in this article I will explain how to keep the DC from the primary windings for those of you who want a flatter frequency response. Using the push-pull Hammonds will cause a slight rolloff below about 50Hz, but that is close to the limits of the speakers I am using, so it does not cause any problems. I realize that PP transformers are not quite suited for single-ended circuits, because the SE units have an air gap in the core to keep it from saturating with DC. I used the #BR-1 speakers from Parts Express, which, although not super high efficiency, sound really good with this amp.

I had some Hammond output transformers handy, #1645, and the load of the primaries on these transformers gave me the necessary load for the 6BQ5s into my 8Ω speakers. It held all of the components and has a nice open look, giving the tubes good spacing for keeping things cool (Photo 1).

I ordered a chassis from Antique Electronics Supply (AES, ) and found that the Hammond #H1444 was the perfect size at 12' x 8' x 2'. The 6BQ5 sounds great in push-pull, but what would it sound like in single-ended triode mode? I had a few of these tubes in stock in my hobby room, so I dug out the parts I would need. I have built some push-pull amps using this wonderful, hard-working little tube, but even though they were fairly simple in construction and low in parts count, I wanted to build one for first-time builders, and one that would sound really good. (All tube model, unpainted chassis.)Ī friend of mine, Neal Haight, who has contributed many of his great ideas to this magazine, recently mentioned a lack of articles regarding what I consider to be the king of the “baby bottles,” the 6BQ5/EL84 power tube.

6aq5 tube amp