Tube Amp Archive

Hey thanks! That makes sense. The earlier Bassman 6G6 used the same scheme as the AB763 amps. Just wondered why they switched.

Thanks again.

Hi all. Question regarding mixing resistors. On all AB763 amps, the 220K mixing resistors are fed by the coupling capacitors which then feed the PI. On all Bassman amps blackface and on, the 220K mixing resistors are placed before the coupling cap(s) that feed the PI. Is there a sonic reason for thi...

http://youtu.be/wUvqSRXWRvc

Another good speaker shootout, featuring alot of the popular choices thru a pretty crunchy amp.

Hey guys. I'm building a Gretsch 6162 type amp, 6973 power tubes and 2 x 10" speakers. Not going for the usual Zep tone, but more Carl Perkins rockabilly tone. Anybody have any good speaker suggestions? Looking for twangy-clean with some hair on the edge. I'm thinking Weber alnicos, maybe mix a smoo...

The trem actually becomes noticeable quite early in the knob rotation. Definitely more pronounced with the NFB lifted. Put the amp in a cab and hooked up a Weber 12A150A, sounds pretty amazing. A different feel than a PR with fixed bias, but not over-the-top distortion like I expected. Actually abou...

I thought about putting a pot in series with the NFB resistor to make a Presence control, still might. But I'm kinda digging the switch. Goes from warm Blackface to kick-in-the-pants Tweed hair with the flick of your finger. I was worried that the Reverb and Trem would bug out when dialing down the ...

Well, had Orange Drops in the phase shift positions. Pulled all three and replaced with some Circle D ceramic discs. That was it! It's a little weak, even with a 470K resistor in place of the 1 Meg depth control. But when I lift the NFB, WOW! Real deep. Still gonna tweak the phase shift cap values a...

I was trying to put off replacing those. I overbuilt this amp, all 1 watt carbon film resistors and 600 v orange drops. But there must be a failure, especially since it worked fine at start up and then just quit. For the build, in order to slow down the tremolo, I started with .02 uF where it called...

It swings from about .037 to 0 vdc (270K - 230K ohms).

With the Intensity set on 1 I have .03 ohms at the junction of the feeders. With Intensity on 10 I have 212K ohms.

Good morning. Well, I went back to the 330 ohm cathode bias resistor on the 6V6's. Measured 26.8 volts from pin 8 to ground, 392 on the plates, and hooked up my bias meter which read 40 mA for each power tube. I believe the range for cathode biased amps is 35-45 mA, which puts me right in the middle...

Okay. Should be 1/3 VAC of the cathode of V4 or the 6V6's?

This is true with fixed bias amps. Is is the same with cathode biased amps? This is the first time I've built a PR with cathode bias, so I'm kinda working with a new set of problems.

Yes, it is fluctuating. Not a huge swing, but something.

The amp evolves! I fixed the lead dress around the reverb driver (was the wire between pin 6 and 1). 12AT7 is back in and quiet! New development...I lost my tremolo. Rechecked voltages and connections. With 29.3 volts from 6V6 pin 8 and ground (remember...this one is cathode biased), and 404 VDC on ...