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Old 3rd January 2004, 01:25 AM   #11
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Hi Guys

I was running three NOS RCA Blackplate 5963s in parallel (six triodes) per channel in a plate loaded triode config before ripping it all out and trying the 6C45pi. Despite having very nice components (remote PSU with dual mono transformers, Shallcos, BGate caps, corian box, etc) the bass was a bit shy and it lacked dynamics compared to my EAD processor...it was also pretty microphonic.

I've now got two of the 6Cs in there alone, and I am very impressed with the results. 170V plate voltage (higher than spec but told this is OK, check the size of the plates out!), 40mA current (must try lower currents later based on the last reply, thanks!), 47R cathode with 220uf bypass. I used 100R AND ferrite on lead to grid and interconnected grids with a ferrite on the lead also. No oscillation problems at all. Bass is heaps better, dynamics are incredible and there is more gain than I know what to do with. The non microphonic nature of the tubes is also excellent.

I have been trying different heater voltages also, and seem to prefer higher than 6.3V than lower. YMMV. This counteracts the slight brightness that is mentioned earlier in this post. It seems more fleshed out at say 6.5V I believe.

Well worth trying guys, IMHO and cheap too

Cheers, Kendrick
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Old 3rd January 2004, 10:56 AM   #12
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Konnichiwa,

Quote:
Originally posted by Silver Stealth
it was also pretty microphonic.
This suggest you had oscillation. The 6S45 is about as dead sonically when pinged as it gets. If it's microphonic, you have oscillation, trust me.

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Old 3rd January 2004, 09:55 PM   #13
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Thanks for the tip, just wish I had a CRO to verify.... Fortunately I do have access to one occasionally so I'll investigate further.

Interestingly enough, when I tried the 82R/68uf cathode R/C combo the plate voltage went up which I thought was unexpected (from 47R/220uf). Can someone explain this? I was hoping to simulate in TubeCAD but the tube isn't in the database and I don't seem able to add the 6c to it either.

Also this new R\C combo did lead to oscillation in the right channel. Major bummer

I have seen about a 10V difference in plate voltage between the channels which I assume comes back to the unmatched tubes.

Cheers, Kendrick
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Old 3rd January 2004, 10:13 PM   #14
EC8010 is offline EC8010  United Kingdom
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6C45pi is a cracking little valve with super linearity, but it needs care to stop it oscillating at VHF. Decouple the HT locally, use a carbon-film grid-stopper, and if you use it as a cathode follower, add a cathode-stopper. It needs a bit of current to wake it up, but 15mA is quite sufficient. I don't believe the 7.8W rating from that envelope at normal temperatures, although a gentle draught of air at -50C (temperature at 50,000 feet) would comfortably enable the rating.
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Old 4th January 2004, 12:08 AM   #15
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Hi and thanks for the tips EC8010...

I decoupled the HT (1000pf/1000V ceramic) and also removed the inter grid wire with ferrite I added earlier. I then added a ferrite on the cathode lead as well, and it seems to have cured the oscillations using the 82R/68uf cathode R/C combo (at least for the last five minutes I've been listening to it!)
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Old 4th January 2004, 12:14 AM   #16
mcs is offline mcs  Denmark
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Quote:
Originally posted by Kuei Yang Wang
BTW, the E180F is in current production and makes a good "pseudo 417A".
Still in current production? Who, where, why?

I bought some of them when they were on sale at AES, but I haven't done anything with them yet. I have used the 417As in a tape head preamp though...

Best regards,

Mikkel C. Simonsen
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Old 4th January 2004, 12:19 AM   #17
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Hi,

Quote:
I decoupled the HT (1000pf/1000V ceramic) and also removed the inter grid wire with ferrite I added earlier. I then added a ferrite on the cathode lead as well, and it seems to have cured the oscillations using the 82R/68uf cathode R/C combo (at least for the last five minutes I've been listening to it!)
And no idea about the bandwidth of this circuit, I reckon?

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Old 4th January 2004, 12:23 AM   #18
EC8010 is offline EC8010  United Kingdom
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Glad to hear it's working. Does it sound any better?
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Old 4th January 2004, 12:44 AM   #19
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Early days yet to say how it sounds, but when it was oscillating it seemed to have lower output in the channel that I believe was oscillating. Now they seemed better matched which is obviously a good thing. Dave Weckl live sounds pretty good...

fdegrove, your brief feedback is appreciated but why not share your knowledge with the team please...forgive me, I'm trying to learn here.

The ferrites chosen were the Nickel/Zinc type catalog no 232-9628 in RS Components, page 922 of the Aussie catalog - these have a 49dB attenuation at 10Mhz, 72 at 25Mhz and 101dB at 100Mhz...if you are implying that this limits the bandwidth are you suggesting these will attenuate in the audible frequency range if used on the cathode or grid leads? Without a curve of their attenuation in the kHz range or a cro handy it's hard to verify...

Keep the good ideas flowing guys...
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Old 4th January 2004, 01:16 AM   #20
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Sound comments as-is

Nitin Sawhney - Migration - Tk 1 - excellent depth. Voice is very airy and natural sounding. Bass may be a touch plummy, but has wonderful texture (and is synthesized so hard to know what it is meant to sound like). No oscillation and nicely centred image. Tabla is nicely palpable - there's a lot to like...
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