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I searched the archives for a DIY 300B project using the FS-030 but have come up blank. Can anybody provide some suggestions. This would be my first scratch build so nothing to exotic please. Would like to try a tube rectified power supply. Would the Cesear II schem work with the FS-030 and EXO-010 (power supply uses a choke with 10H 150mA) Power supply is given in next message below. I don't know how to put two URL's into one message.
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Just ran across this circuit.417 IT coupled to VV30B
http://ken-gilbert.com/building-your-own-tube-amp
MSL
Builder of MagneQuest & Peerless transformers since 1989
Edits: 10/24/11
This one is not too difficult. Sounds great.
Here's a bigger size to get a better look at it.
DanL
This is the Komuru direct coupled 300B design. The driver stage is
the magic.
I use the driver stage (6P5GT / 6V6 triode) on an 845 amp. It steals
the show everytime I audition in in small listening groups. You can
forgoe the 800V supply of this direct coupled design and use IT or
LC coupling between the driver stage and output tube and get outstanding
results at sane B+ (400V)
-- Jim
Hi Jim:
I'd be tempted to use a bit larger of a plate choke on the anode of the triode connected 6V6--- and use an inductor that has been designed as a plate choke.
MSL
Builder of MagneQuest & Peerless transformers since 1989
The 6V6 as a triode driver is a 20ma affair. I believe that Tango had an IT part in their catalog that was precisely built for 6V6 - everyone was using it about 15 years ago. It was either the NC-16 or NC-20... Nonetheless, the 6V6 is a very sweet and clean sounding tube.
Direct coupled amps are really only for people who know what they are doing... Because one tube sets bias conditions for it's neighbor - it's very easy to blow things up when stuff goes wrong (tube out of socket, dead filament, anything). Too easy to destroy something with that topology.. Ontop of that, you are always dealing with a 700-900V supply due to one tubes plate being tied to anothers grid.. So even the PSU becomes hairy and expensive... The Welborne DRD amps use this topology - I'd be anxious to hear about in-field reliability... :)
Nonetheless, direct coupling the first two stages is safe and inexpensive.. LC coupling the Komuru driver sounds every bit as good
as IT coupling on my 845... Cheaper too - but I'd already bought my interstage transformers but I did listen and audition out an LC coupled amp on that driver and it was awesome!
I'd also lower the total gain of the Komuro stage.. It has 20*8 mu = 160.. You could sub out the 6J5 (mu 20) for something
around 10 - using a 76, 6P5 - which is what I do. Omitting the cathode bypass cap on the first will also reduce the net gain... In my implementation, the driver gain is 64 - which is perfect for a 300B or
LV 845 and a 2V input. You might find other ways to modify the net gain - for instance using perhaps the 71A rather than the 6V6. One of the very nice thing about the 6V6 / 76 combination is that the resistor complement needed to set bias is very straight forward - 47K, 470 ohms, 4.7K ohms.. :)
I have been following this post with interest to build also. My question is what would you use in place of the UTC power transformer and the Stancore 30H choke
The UTC transformer is rated 150mA, but only supplies 61mA according to the schematic. That opens up a lot of other transformers, such as the PGP8.1 that Mike makes. The only question is whether the HV supply can be raised 300 volts.
A BCP-15 gapped for 40mA would handle the 27.5mA of the 6V6 easily, and give 50 henries for better bass.
If the PGP8 can take the voltage offset, you could do the whole power supply with the one transformer, by using 1200-v Schottky diodes instead of the tube rectifier. It would no longer be the real Komuru design, but would be easier to build and probably sound very similar.
Just another idea...
Please correct me if I'm wrong... it has been known to happen!!
Cheers
FM
Haha! Well, I don't imagine Mike has lost the drawings ... :^)
Mike has some really nice power transformers in his archives, but his time is limited, and I for one feel that time is best spent on iron that handles audio signals. It just makes more difference there. Lots of people make decent transformers, and a decent power transformer is good enough to make beautiful music. Damn few make excellent audio transformers, and excellent is audibly better then pretty darn good - which is not all that common either. Excellent beats the crap out of decent in audio iron.
Just my opinion, of course.
thanks for the response. It gives me something to think about.
PJ wrote:
"A BCP-15 gapped for 40mA would handle the 27.5mA of the 6V6 easily, and give 50 henries for better bass."
And I could airgap it for 30 madc and get > 50 henries of L.
MSL
Builder of MagneQuest & Peerless transformers since 1989
I've been all over the map looking at schematics of this and that, looking at reviews here and there & at some point I'll have to take a leap and do it what-ever "it" may be although I think this komuro schem may be "it". The schem above looks it fits my criteria although I'm not sure where I would source the UTC mains transformer nor have I found a substitute.
DanL suggestion about 6P5-6L6/KT66 to 300B makes me think his version would be a 300B with "balls" so to speak. I'm not at the stage of subbing tubes into schem's without a little hand holding.
Thank you again.
FM
Close to what I would do.
I would use a 6P5-6L6/KT66 to 300B.
DanL
with a lot on H but smallish current.
To infinity and beyond!!!
The Fi Primer (J.C. Morrison) 300B amp is the classic; the Angela / JE Labs design is closely related. These are older designs, however - there are some useful innovations that have appeared in the last decade or two.
Looking at the data, I find it interesting that the FS-030 running 90mADC reaches it's greatest inductance at 15 watts output. That makes it well suited to a sturdy 300B operated close to its maximum ratings. Even though it is "rated" at 60mADC. (It can muster 5% more inductance at 60mADC/3.3watts - a good 2A3 point).
Most 300B amps will call for a 3K primary impedance and the FS-030 will serve well.
Would the exo-010 work?
Thanks FM
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