I recently bought a Maz18NR mk2. Great tones, very happy with it. But since my band rehearsals are in a (rather small) studio (and live I always mic the cab), I found the stock amp too loud. I experimented with attenuators, but still prefer the ‘direct’ tone from an amp. Long story short: I put a 12AU7(A) (TAD Premium) in V1. I LOVE the tonal result: much less volume, cleaner, same great response - and I get to turn up both Volume and Master without going deaf (currently both around 10 0’ clock, producing about 89-90 dB at 1m from speaker). BUT, here’s my question: will a 12AU7 in V1 cause any unwanted side-effects? Will it require some kind of xtra care?
In the MAZ 18 MKII a 12AU7 in v1 should not cause any electronic issues.
A 12AU7 is a currant source device, that is it will drive a signal very well with little or no increase in amplitude or gain, that is why you like it in the V1 position. The only concern with that tube used in a 12AX7 circuit design is Cathode Currant draw, which is higher on a 12AU7 .
The MAZ 18 NR MKII uses a parallel triode connection and the Cathode Resistor is 1.2K which is on the high side of biasing a 12AX7 so you'll be safe with a 12AU7. A little over your head info, in a Parallel Triode connection you half the value of plate resistor and half the cathode resistor. Using a 1.2 K cathode resistor in this configuration is equal to a single 2.4K cathode resistor , which is what is normally used on a 12AU7. There did totally confuse you by explaining that ?
Post by Chilly Gibbons (Todd T.) on Jan 4, 2019 9:23:34 GMT -7
That's why we leave the engineering to you Doc!!
Z-Lux Combo in Black, Z-Lux Head/1x12 Z Cab in Red, Cure, Maz 8 Head/1x12 Z Cab In Black, another Maz 8 head/1x12 cab in blond, blond Z-Verb, Red Z-Verb, Maz 18 NR MKII in Black, Therapy blonde, Red Monza, Air Brake, and few more now, but who is counting? Past: Monza 1x10 in Red, Mini Head in Red, Maz 18 Head in Black (Baby come back...)
Thanks all for the - reassuring - info! And yes, Doc, I did experience a slight dizzyness upon reading your technical explanation ;-). But I focus on your opening statement, that the 12AU7-type tube won’t cause any issues. Great news, thanks again and keep up the good work! 👍
I think I would go with a 12AY7 instead. That was a common first gain stage tube in a lot of tweed Fenders. Rock players would replace them with a 12AX7 to get more gain. The gain of a 12AY7 is a little more than a 12AU7 but considerably less than a 12AX7. Whichever you use don't expect the amp to breakup at a much lower volume. It will just be quieter at the same control settings and the tone may be a little warmer. A guy I tech for plays with a jazzy tone and I put a 12AY7 in his first stage. He likes it better than a 12AX7. It breaks up later. Some folks would call that more headroom.