• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

OTL designed by Tim Mellow with 4 6C33C?

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atmasphere

atmasphere

Member
Joined 2007
atma-sphere.com
dwhitf said:
I have been buying NOS Johnson 247 ceramic sockets off ebay
sometimes called RCA UT-106.
A .125 drill deck,fan on each socket and a heater mod like the Graff GM20 otl (thick runs of metal then
attach to heavy duty wire, metal is a heat sink i guess).
Sockets lowered so air can pass by,aluminum spacers to transfer some heat to the deck also.

Any anymore ideas?

Comments appreciated
Darrell/dwhitf
Click to expand...

Make sure the hole for the socket is large enough that air can pass by the tube once it is in place.

Its really the filament connections that you have the most troubles with. It seems that if you run them in series the wire you use will not be so prodigious (although it is important for the wire to be heavy so it can carry the heat). I used to make a little heatsink that went between the middle pins to help them cool off. Use SN96 or similar high temperature solder, and Teflon-coated silver wire is a good idea (avoid Teflon-coated wire that has silver-plated copper, it will not sound right, although for the filament connections I would not worry about it).

Although noisy, the fan ideas mentioned earlier will make this go a lot easier. OTOH, it will not take a lot of rpm from the fan to significantly cool things down.
 
S

sampleaccurate

Member
Joined 2010
atmasphere said:
Before using any 6C33 they should be pre-conditioned for at least 3 days and nights by running the heaters with the plates, cathodes and grids tied to one side of the heater circuit. This will minimize arcing and double the life of the tubes. BTW this is a good idea for 6AS7Gs too!
Click to expand...

Wouldn't you know it, I was just getting on here to ask, and there's my answer - thanks. I'm setting up a test rig for my 6H13C and 6C33C tubes and I want to burn them in first but wasn't sure how.

Also interesting stuff about the separate cathode followers if 6C33Cs are used.

Does anyone have experience with the Chinese ceramic 6C33C sockets with the gold plated contacts? Those are what I bought, and they look good, but I have no idea how well the gold plating will hold up to the heat.
 
D

dovla

Member
Joined 2010
Schematic with 6s41s

nafunga said:
Thanks all for your comments - Yes, the box is a Cutlery box - various sizes around at 'boot fairs' etc. One thing I didn't mention in my report is that the box only contains the two transformers for heater supplies (In order to keep the size down - the power for these and the +&- 150v ht's is derived from a 500w isolation transformer (hidden behind a setee!)(extra points for that from wife!) There is a 3 core cable between the two - L,N & E. This probably would't be practical for the higher powered version
As to the DC offset - after a weeks run-in, it seems to settle at around ' +&- 0.005v'! Amazing! This extremely good stability may be in some part due to the lower power 6C41C's - not sure if 6C33C's would be this good (?) My previous OTL using 6C33C's certainly wasn't! Like to know what other builders are getting?


Regards,

David.
Click to expand...
Can you post the schematic as built with 6s41s tubes? I was also thinking of using a 500W step up/down transformer externally - it has it's own housing and is rather bulky so nice to hide it somewhere.
Any reasons against using halogen light 12V= electronic transformers (rated at 105W on the 12V side = 8A approx) to power 6V heaters in series?
 
N

nafunga

Member
Joined 2005
Can you post the schematic as built with 6s41s tubes? I was also thinking of using a 500W step up/down transformer externally - it has it's own housing and is rather bulky so nice to hide it somewhere.

Schematics is exactly as for 6C33C's, except for points I mentioned earlier and for smaller 6S41C heater transformer. Sorry, I haven't tried electronic transformers but can't see why not. There is absolutely no hum with this design so shouldn't be a problem. I used ac heating all round and don't think dc to the Ecc83's is needed.

P.S - Still working well with no bias or balance issues! Well done Mr Mellow!
 
D

desperateaudio

Member
Joined 2004
desperateaudio said:
Next for me is the Rozenblit OTL from Audio Reality. I will be starting that today. Hope you enjoy the sound of the amp!
Click to expand...

Well as promised earlier in this thread I did build the Rosenbilt 150 watt OTL amp known as the T8 I believe. I am using 8 6LF6's as opposed to EL509's. They are the same tube just different bases, actually the 6LF6 is a bit tougher. The amp is amazing. The bass is tight the sound clean but with life and layers. This one is making it from the breadboard to the nice case tomorrow. I will upload some pic's soon for those interested. The bottom line is that this amp is warming up to matching the sound of my NYAL OTL3's.
 
tympani1d

tympani1d

Member
Joined 2009
desperateaudio said:
Well as promised earlier in this thread I did build the Rosenbilt 150 watt OTL amp known as the T8 I believe. I am using 8 6LF6's as opposed to EL509's. They are the same tube just different bases, actually the 6LF6 is a bit tougher. The amp is amazing. The bass is tight the sound clean but with life and layers. This one is making it from the breadboard to the nice case tomorrow. I will upload some pic's soon for those interested. The bottom line is that this amp is warming up to matching the sound of my NYAL OTL3's.
Click to expand...
Yes, please.
 
T

thelegr

Member
Joined 2009
Hello guys!

im planning to make an tube amplifier.... i have a very small budget so i decided to make an OTL amp....but as im an begginer in DIY CONSTRUCTIONS
i need some informations...

which has better quality: Push-Pull or OTL?
Is this a quality amplifier?
what will be the total cost?
Do you have any better but cheap project to suggest me?

Thank you in advance for your time.
 
B

banat

Member
Joined 2009
Since You are DIY begginer and Your financial budget is small Avoid the the tube OTL Amp for Your first Tube Amp project !!!

Here on this DIY Audio forum You can find many other `conventional` tube Amp projects, much more simple and cheaper than OTL Amp, with relative good sounding results,but OPT coupled.
Of course : Nothing can beat an tube OTL Amp sound !!!

Best Regards
 
T

thelegr

Member
Joined 2009
look, im not completely begginer... I've made an amp with LM3886 and I've helped my dad with his own tube amp (KT88 PUSH-PULL Ultralinear in AB1 Class 2x37w).

So i wanted to make an tube amp for my room(i have good speakers)

Which is cheaper, OTL or Push-Pull/Single Ended (and others with output transformer WITH 6C33C-B)?

something better+cheaper (allways with 6C33C-B)
 
B

banat

Member
Joined 2009
Last edited:
atmasphere

atmasphere

Member
Joined 2007
atma-sphere.com
thelegr said:
look, im not completely begginer... I've made an amp with LM3886 and I've helped my dad with his own tube amp (KT88 PUSH-PULL Ultralinear in AB1 Class 2x37w).

So i wanted to make an tube amp for my room(i have good speakers)

Which is cheaper, OTL or Push-Pull/Single Ended (and others with output transformer WITH 6C33C-B)?

something better+cheaper (allways with 6C33C-B)
Click to expand...

I made an OTL as my first amp. I did know how to solder, and I did it because I could get the power transformers cheaply and didn't have to pay for an output transformer. Its my opinion that it is still possible to do this today, although inflation has changed the price of everything. I built that first OTL for about $200.00. Today I think it might cost about $600-$800. It made 50 watts per channel into 8 ohms and used 8 6AS7Gs per channel.
 
T

thelegr

Member
Joined 2009
atmasphere said:
I did know how to solder,
Click to expand...

I Know how to solder too. As i told you i ve made my own amp with LM3886 ICs and i've helped my dad with his own tube amp.

atmasphere said:
and I did it because I could get the power transformers cheaply and didn't have to pay for an output transformer. Its my opinion that it is still possible to do this today, although inflation has changed the price of everything.
Click to expand...

That's why i want to make an OTL Amp!!


For everyone who knows Greek, i learned a lot of things for OTL amps from here
 
T

thelegr

Member
Joined 2009
thelegr said:
I Know how to solder too. As i told you i ve made my own amp with LM3886 ICs and i've helped my dad with his own tube amp.
QUOTE]


In addition i've built a lot of kits, and i've desoldered a lot old machines. I've repaired my audio mixer's graphic EQ) too. my dad knows some things on electronics and he can help me too

the reason that i want 6C33C-B is this


As i told you, if you have something cheaper (i can build something better when i have biger budged) to suggest me with those tubes just do it
Click to expand...
 
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