Finishing up another pair of the Inspire Speakers in Karelian Birch...
 

https://live.staticflickr.com/65535/...b41aacbe_b.jpgUntitled by analog addict, on Flickr

https://live.staticflickr.com/65535/...63864aee_b.jpgUntitled by analog addict, on Flickr

Check out the close up of this wood grain. In person it's almost three dimensional. These are seriously beautiful speakers, and they sound better than they look. With a PSE 300b, the sound is absolutely out of this world. It left Dennis' and my mouth hanging open...


https://live.staticflickr.com/65535/...d451326e_b.jpgUntitled by analog addict, on Flickr

There is an AA member who has first dibs on these, but if he passes, they will be available to the general AA public on the marketplace

Correct

Sent

I have a standard Inspire 300B-v amp and have a few questions maybe someone here can help me with...

1.) Is this amp able to use a 5AR4 rectifier or 5R4WGY instead of the 5U4 shipped from Dennis? Just curious as to what rolling the rectifiers will do to this circuit? Or should this be avoided?

2.) Also, how about going from the 6SL7 over to a 6SN7? Would this be possible and/or serve any purpose?

3.) I was thinking about buying some Zu Audio speakers with 16 ohm impedance. Would the standard Inspire 300B-v need to be sent back to Dennis to have the transformer leads changed to run better with a 16 ohm speaker? I'm currently using the amp with Soliloquy 8.2 speakers, designed and built by Dennis in 1998.

Thanks for any help.

Dennis says take the interconnects from the preamp and switch them to see if the problem changes channels. If yes, the problem is upstream.

if no, remove the interconnects so there is no input signal and if it goes away, it's coming coming from upstream.

If still present without any upstream signal, turn the amp off and pull the 6SN7/driver tube. Then turn it back on. If the problem goes away, it's the driver tube.

If no, turn the amp off, leave the driver tube out, and then swap the output tubes right to left and vice versa. Lastly, if the problem is still present, replace both the output tubes.

If the problem is still present after all these tests, we can make arrangements to send the amp in for service.

I have forwarded Dennis your questions and have not received a response. He apparently has a bad head cold and is not feeling 100%.

Here are my thoughts on your questions.

1) I would think a 5R4WGY would be fine since the voltage drop is very close to a 5U4. I would not try the 5AR4 without direct approval from Dennis since it drops the least voltage of the normal rectifiers, and may drive the B+ voltages higher than intended. Of course he may turn around and say no problem. - EDIT- he said the 5AR4 is fine for the amp, but he likes the sound better with the 5U4/274B/5R4 rectifiers.

2) In general, most amps Dennis uses wont be hurt by swapping 6SL7 to 6SN7 and vice versa. Since the 6SL7 has a relative gain of 100 and the 6SN7's gain is 20, you may notice drop off in gain. Or the circuit may have absolutely no issues with either. A lot of times a 6BX7 is also OK, but since I have no experience with this tube, I won't risk a comment.

3) Tube amps are much less sensitive to output impedance than SS devices. Anything between 4-16 ohms will work fine. However, again, you may notice some differences in gain.

Analog Addict,
Thanks so much for the response. I definitely appreciate your advice and speaking to Dennis. Hopefully this information not only helps me, but also other owners of the 300B-v amplifier.

Well, you can do me a favor and give us your listening impression of the 300b-v. I’m sure folks get tired of hearing me talk about them all the time..

The 300B-v is my only single ended amp in my collection right now. I personally use it direct, one source, with the built in gain adjustment knob. It sounds just beautiful for low volume listening. When the family is sleeping and everything is quiet, there is just nothing like it. Midrange is so natural yet detailed at the same time. Not one hint of harshness, ever. The midrange just sounds so natural and sweet with this amp. It's almost like the difference between a singer singing out of an amplified system with PA speakers vs singing in your living room, unamplified, quiet and direct, etc. Hopefully that makes sense. I need to get some more efficient speakers to give a proper review. I'm still using the factory tubes Dennis shipped with it. No plans to change the Western Electric 300B's. I wouldn't mind changing out the Russian 6SL7 or playing around with the rectifier, hence my questions above. And the 16 ohm Zu Audio speakers look tempting to me. I was just concerned that the 16ohm impedance might not be ideal for my 300B-v amplifier. All my other tube amps have taps for 4 ohm, 8 ohm, 16 ohm. Beings Dennis uses single taps, I was debating whether or not the Zu speakers would be a great match.

I think I read that the output impedance on the KT88 Firebottle is 9 ohms? My 4 ohm nominal speakers sound amazing with it though.