Couple of questions about the finished build.

[currly30]

Just finished the build. Everything is working great!

I had a couple of tube questions.

If in the future I want to swap the 300B. Should I do the Hum Balance again?

If I swap the 5670 tube. Will I have to adjust the potentiometers on the the C4S boards again?

From what I read 300Bs need a burn in time to sound there best. Is there a certain way, if needed, to burn in the 300B?

[currly30]

When I eventually replace the .1uf 630V cap, the 10uf 630V cap, and the 100uf 250V cap. What is the acceptable voltage range for replacement caps or do I need to make sure I get the same voltage for all the replacement caps?

[Paul Joppa]

Just finished the build. Everything is working great!

I had a couple of tube questions.

If in the future I want to swap the 300B. Should I do the Hum Balance again?

If I swap the 5670 tube. Will I have to adjust the potentiometers on the the C4S boards again?

From what I read 300Bs need a burn in time to sound there best. Is there a certain way, if needed, to burn in the 300B?

Yes, you'll need to re-adjust the hum balance on the 300B.

Yes, you'll need to re-adjust the 5670 plate voltage.

To burn in the tubes, just run the amp for 50-500 hours; no special technique. Two things happen - the cathode finishes "forming," and the getter ties up any residual gas. Tubes built for longer life need more time to fully form the cathode, hence the range of time.

For the signal-path capacitors and output transformers/plate chokes, usually 50-100 hours of music playing does the job - except for Teflon caps, which can take 200-500 hours.

These are all empirical findings and will vary quite a bit.

[Paul Joppa]

When I eventually replace the .1uf 630V cap, the 10uf 630V cap, and the 100uf 250V cap. What is the acceptable voltage range for replacement caps or do I need to make sure I get the same voltage for all the replacement caps?

Yes, all the caps must be rated for at least the original voltage. Higher voltage ratings are acceptable.

[currly30]

Okay, good to know that I can just leave the amp on to burn in the tubes.

It is a lot easier to find higer voltage caps than exactly 630V caps. Is there any wiggle room on the uF rating for the .1uf capacitors or should I make sure to get the exact same uF rating?

[Paul Joppa]

600v is close enough to 630. I'd prefer 800v, but they are not common, and we've never had a problem with the 630v caps. I'm just a conservative engineer  :^)

The 0.1uF cap is more flexible; I'd say between 0.047 and 0.22uF will only make a small difference in the deepest bass.

The 10uF parafeed cap is similarly flexible. It will interact with the connected loudspeaker, so experimentation is better than prediction. The range is similar to the 0.1uF - 4.7uF to 22uF is reasonable. The smaller cap will lose some of the deep bass but handle overloads a bit better; the larger cap will extend the bass but will overload more easily.

[currly30]

Interesting. I will have to keep that in mind while looking for caps.

[currly30]

IS 400V okay for the 100uf cap?

[Paul Joppa]

All the caps must be rated for at least the original voltage. Higher voltage ratings are acceptable.

400v is higher than 250v, so that is fine.

[currly30]

Thanks. I thought that it would work but figured I should ask before buying caps.

Had another question. If I use 6SN7 style tube for the input tube does it reduce to total output power of the Kaiju?
If so, how much does it reduce the total output power?

[Paul Birkeland]

You lose a bunch of gain if you do that, so it's not the best idea. 

[Paul Joppa]

It does not reduce the maximum power.

[Larpy]

I'm a fan of the 6SN7 (I converted my Foreplay III to use them instead of the stock 12AU7s), but it's not a good tube to drive 300Bs.  Various 300B amps have used it as a driver (JC Morrison's circuit, Joseph Esmilla's), but the 5670 works much better.  Better to try different 5670s (I like older RCAs myself) than to switch to another tube entirely.

[currly30]

Interesting. I will look into some 5670 tubes. The stock ones do sound pretty good. Does the 300B make a larger difference than the 5670?

[Larpy]

Hard to say.  With 300Bs, I've tried the stock EH, Genalex, and new production WE.  The EH and Genalex sounded pretty much alike but the WE is in a whole different league, but for $1500 a pair they damn well better be.  Is the improvement in sound commensurate with the difference in cost?  Probably not, but I'd say they're at least twice as good (though I don't really know how to quantify such judgments).

With 5670s, I've tried the stock GE (1980s production), older GEs (1950s), Sylvania 2C51s, a pair of WE 396A, and older 3-mica RCAs.  I like the RCAs the best, but I could live happily with any of them except the WEs.  They sound underwhelming.

Tube rolling 300Bs gets expensive quickly.  5670s are pretty cheap (within the context of vintage tube prices anyway), so that's where I'd suggest you experiment.