Glasshouse 300b SET

pre65 · Post by **pre65** » Thu Jan 13, 2011 4:08 pm

After Richards rapturous prose (WD forum) on his Glasshouse 300b SET I checked out the circuit on the HFC web site.

http://www.hificollective.co.uk/kits/pd ... t_icrt.pdf

I notice it has a negative supply for the cathode follower which I seem to remember Nick saying was a good idea.

So, has anyone here ever had one, or used this circuit, and if so what opinions ?

Mike H · Post by **Mike H** » Thu Jan 13, 2011 5:28 pm

Can I express an observation if not had one?

Ah allows DC coupling without o/p cathode being rediculous high Volts.

Post by **Nick** » Thu Jan 13, 2011 5:47 pm

I notice it has a negative supply for the cathode follower which I seem to remember Nick saying was a good idea.

Not so much a good idea, but a essential one if you want to run the output valve cathode at 0v and have the directly coupled grid at a -ve voltage.

Mike H · Post by **Mike H** » Thu Jan 13, 2011 5:49 pm

Which WD topic is this?

pre65 · Post by **pre65** » Thu Jan 13, 2011 5:52 pm

I fink it's zis wun.

http://www.world-designs.co.uk/forum/sh ... php?t=5801

Mike H · Post by **Mike H** » Thu Jan 13, 2011 5:55 pm

Oh right, that's the one I just read. Just wondered if there was another one

Mike H · Post by **Mike H** » Thu Jan 13, 2011 5:58 pm

2nd obsvervation ~ it's spookily similar to my first 300B SET I made, loosely based on PSE300, tho that was EF37A > 6SN7 CF, but cap coupled to 300B grid.

Dave the bass · Post by **Dave the bass** » Fri Jan 14, 2011 10:17 am

Aaaah! so thats why the CF has a split rail supply.

DTB

IslandPink · Post by **IslandPink** » Tue Jan 18, 2011 6:56 pm

My friend Len just bought one 2nd-hand from someone.
I heard it, it's OK, he needs to improve a few dodgy components in there .
I can give you a better assessment in a month or two if you like. I have no reason to believe it'll sound better than C3m>300B though

Personally I think with a bit of improvement in the WAD circuit , if you wanted 8W-ish you'd be better with Parallel 2A3's . I have never managed to get any 300B amp to sound as good as a 2A3 or a 211. Of course Paul Barker told us this several years ago !

Post by **Nick** » Tue Jan 18, 2011 10:32 pm

IslandPink wrote: Personally I think with a bit of improvement in the WAD circuit , if you wanted 8W-ish you'd be better with Parallel 2A3's . I have never managed to get any 300B amp to sound as good as a 2A3 or a 211. Of course Paul Barker told us this several years ago !

I did once

Dave the bass · Post by **Dave the bass** » Tue Jan 18, 2011 10:35 pm

Nick wrote:
I did once

What happened?

DTB

Post by **Nick** » Tue Jan 18, 2011 11:50 pm

I kept changing it, and then realized I had lost the magic several changes back, and never managed to get back to the good place again (yes, I just realsied that sounds like Zero's story), Ali heard it when it was good, it wasn't imaginary.

simon · Post by **simon** » Wed Jan 19, 2011 1:00 pm

I was one of the lucky few to hear Steve's 300As in Nick's 300B amp - still the best sound I've ever heard.

Post by **Nick** » Wed Jan 19, 2011 1:53 pm

The amp you heard the 300a in had passed its peak by then

Mike H · Post by **Mike H** » Wed Jan 19, 2011 2:08 pm

IslandPink wrote:My friend Len just bought one 2nd-hand from someone.
I heard it, it's OK, he needs to improve a few dodgy components in there .
I can give you a better assessment in a month or two if you like. I have no reason to believe it'll sound better than C3m>300B though

Personally I think with a bit of improvement in the WAD circuit

One possible reason is the EF86. Seems like everything I've done with an EF86 in the front end all sounds like, er well, like it's got an EF86 pentode in the front end. It seems to stamp its own personality on everything.

EF86 is an (by now) old noval "upgrade" (mostly amounts to just make it smaller) on the even older octal EF36.

I was using EF37A (the "super-dooper" version of the latter) and even then I noticed (by measurement) the HF response starting dropping off below 15 kHz

Maybe 'cause it's got a huge Ra, 2 Megohms in pentode mode.

OTOH it seems to be a quite different pail of whelks triode wired, not too bad acrtually, Ra = 10k, mu = 20. IIRC. Which may be why I've noticed several instances of folks on the web advising using it that way.

There may also be a problem with the paralleled CF, if poss I'd wanna try getting it down to a single triode.

audio-talk

Glasshouse 300b SET

#1 Glasshouse 300b SET

#2

#3

#4

#5

#6

#7

#8

#9

#10

#11

#12

#13

#14

#15