audio-talk

Observe and Drool :

http://www.tubecollection.de/ura/postroehren.htm

MJ

7N7 and 14N7
Despite the name , the filaments are actually 6.3v and 12.6v .

...and you can get the nice silver-plated/teflon sockets for not too much money .
Talk to Gerry at Crowthorne Tubes .

MJ

I can send you the circa.2006 circuit of the C3m-300B if you like, will make it clearer .

MJ

I rather like the look of the C3m/C3g as-is , if you can get nice ones with the proper paper band labelling round the bottom that is . I think with one big output valve , a VR tube and a C3m in black casing, it's a nice combination . Variety is the spice of life .

ILPS

I just read 20v 25VA - why do you need that much ? Work it out - 20V x 0.125 x 2 x 1.41 = 7VA . So 7.5VA toroid is enough , and a 15VA gives you plenty, so you can throw away some in making a DC supply if you absolutely have to ....but try it AC first , it's not like a phono amp here .

MJ

DC absolutely unnecessary with this ( unless you have 108dB horns or something ? ) . Small ( 7.5VA maybe ? ) toroids from RS or Rapid with 2x 18V secondaries give over 20V at 0.125A with my 247-ish mains supply - I had to add series R in the mains side to drop to my preferred case of a slight under-...

Got a blockage in the email , so I can't send the circuit diagram (I scanned at work) to you just yet. Should be soon .

Ah yes, I'd best have your home email Phil, think the file is over 1M .


I should have put a copy in the post .

Mark

That table is confusing, and I'm not 100% sure Jac knows what he's talking about there . The gain for the C3g in triode is about 40, and for the C3m in pentode with about 12k or 13 k would be 78 as shown . However, gain of the C3m ( mug1g2 ) in triode is 19 from memory . To calculate the gain in pen...

More gain than the g ? It's the other way round , generally , the C3g would have more gain than the C3m . As a triode C3m has about 19 , C3g is 40-something . C3g has more transconductance than C3m so will have more gain as a pentode too , but you can easily have too much gain with a pentode . I use...

C3m heater - just get a small toroid with 2x18v secondaries - the voltage comes out at 20v anyway .

MJ

Hello Steve Please elaborate ... The differences were subtle . I didn't say anything about distortion , just that there was slightly more tone and refinement at the top end with the pentode . The bass was also a bit out-of synch with the rest ( subtle effect again ) at times . I was a little surpris...

C3m it was Phil . I never quite decided how to use C3g in the context of the 460V B+ , because the max dissipation of the C3g is lower , and the gain would tend to be very high with the typical 11 to 13k anode load . I thought I had the circuit on my thread about 'future plans for 300B XLS amp' but ...

Ian
Have you got a picture of the internal layout of your F4 ?
I'm looking to build one very soon , might solve a few questions I have as I go along . Nick didn't have a pic to hand .
Mark

Andrew I haven't bought the ribbons yet ! I'll have to wait until I can sell the old car ! I'd be interest to find out where to buy them cheapest . Currently I have horns awaiting delivery from Australia and two compression drivers awaiting final parts to be finished and sent from Oklahoma ...oh and...

Hi Lee You know, I did look at the Klipsch, and things like Christian Rintelen's Blue Thunder hybrid front/rear-loaded 15" unit in SP, but there are some problems. Anything with pure horn-loaded bass has to be HUGE to get down much below 100Hz. On those hybrid schemes like the blue Thunder or t...