If he's going to build what's been prototyped, it would run either/or 6J5s or 6C5s. These are essentially half of a 6SN7, but are older and can be found in the ST shape. I can't wean Dennis off of new manufacture tubes completely, but I keep trying.....:D

Found a pic. On the left is a LP-27. On the right is the new prototype, tentatively named the CJ5 or perhaps CJ5'er because it uses both 6C5 and 6J5 tubes....

https://live.staticflickr.com/65535/...3702323d_z.jpgUntitled by analog addict, on Flickr

If it's the amp that was sitting on his table burning in the last time I was at the shop, the rectifier isn't going to make a difference on the choice of driver tube. It will depend on what output tubes you want to use. If you're using 6550s or KT 88s or larger, use the 5AR4. If your'e running 6L6Gs or 6V6 or smaller, use the 5U4. As I recall, we also used a 5V4 for a set of 1945 vintage 6L6GAs

Absolutely agree!

I noticed that listing. It is a little tempting. Not much of a jump in power from my Inspire but would be running the output tubes more in their optimal range than in mine, where they are pushed to their max.

Attachment 63010

Looks like the new Inspire CJ5 preamps are getting close. Raw chassis soon to be at the powder coater. I have been enjoying a prototype here at home for a few weeks. I’ll share my thoughts soon.

New amp makes slight noise-Do I Have Crappy Power?
 

I've had my Fire Bottle KT88 amp for just over a week and absolutely love it. The sound-stage it throws is wider, deeper and taller than my NAD solid state. Detail is great and performers are where they should be. Dynamics are great and power seems more than enough. It is exactly what I am looking for, except for 1 thing, a slight hum coming from the amp and speakers.

The hum is very slight and doesn't change with volume. It's virtually the same with the passive preamp connected or with the amp just by itself. It seems to change from day to day or time of day, with evenings generally being "noisier" than during the day. Most of the time I have to put my ear within 6 inches of the speaker to hear it but sometimes I can hear it from my listening position (usually at night). The hum doesn't destroy the listening experience as it isn't obvious once the volume is up a bit but every once in a while I can hear it between tracks, etc.

I messaged Dennis about it and he indicated that the amp was perfectly quiet during testing and listening, and I believe him. I'm sure he knows how to design a quiet amp. I guess the amp internals could've been damaged somehow during shipment but my assumption is that it's related to the wiring/power supply in my house. Dennis suggested I "float the ground" to see if that got rid of the hum. At first I thought it helped but now I'm not sure. I ordered a Hum X from Amazon to see if that would work and so far it doesn't seem to make much of a difference. I've tried all sorts of combinations and so far the quietest is with all components plugged into a power strip, the Inspire plugged into the power-strip using a "cheater plug" and the strip plugged into the outlet through the Hum X. The hum is reduced but is still audible from a foot or two away.

At this point I'm wondering if I just have "crappy power" that makes itself known through the amp. I haven't experienced hum with any of my past solid state amplifiers but they had much smaller transformers and used 2 prong plugs, if that makes a difference. I've seen some people on other forums having issues with DC offset. Maybe that's what I have?

Assuming I have a DC offset I'm tempted to try a Emotiva CMX-6 which is supposed to handle DC offset issues. That's the only other thing I can think of.

Any other ideas or experience that anyone can share? If so, I'm all ears!

I dropped off the CJ5 chassis at the powder coater today.
They should be ready next week.

Try listening for hum with nothing connected to the amp except the speakers. If it hums, try turning the volume up and down and see if the hum varies with volume. Can you tell if the hum is 60 or 120 HZ?

I've done a bit more experimenting to see where/how the hum is coming from.

It is present with just the amp alone and doesn't change with volume or the addition of the preamp. I'm pretty sure it is 60hz, it's lower and less "buzzy" than 120hz.

The interesting part is that it seems to be loudest when first turned on from cold. After about 15-20 minutes (when the amp is starting to get warm) the hum is much less prominent but still there. Also, the hum is lower in volume when I use the "cheater plug" while the amp is plugged into the power strip along with all the other components. When the amp is plugged into an outlet by itself the hum seems to be louder. I'm going to test this again over the next couple of days to see if it is repeatable, just to be sure.

Is this a combination of a ground loop and noisy transformer caused by some other power anomaly? Are transformers typically noisier until they warmup?

I communicated with Dennis and he said take the three prong cord and a pair of pliers and break off the ground plug, which is the bottom round prong. That is floating the ground.

He them said to take the now two prong plug and flip it over so that it is oriented in reverse from the normal orientation when it has three prongs. This is called reversing the polarity. Now test the amp and see what happens.