2018 Carverfest Tube Power Amplifier Build

12th Annual CARVERFEST 2018 September 5th - 19th
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Snoop65
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Re: 2018 Carverfest Tube Power Amplifier Build

Post by Snoop65 » Tue May 08, 2018 5:50 pm

MRHP wrote:
Tue May 08, 2018 4:52 pm
Just making sure that the EL34 / 6CA7 type tube will work in this amp??

Without tube socket changes??

Just bias adjustment only??

Looking at some Mullard xf2 EL34 1965 vintage nos tubes.

SNOOP help a brotha out I got the tube fever and the only cure is more vintage tube smell!!!
I got the tranquilizer gun and the straight jacket ready Eric! No worries!!!! :lol: :lol:
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Re: 2018 Carverfest Tube Power Amplifier Build

Post by UncleMeat » Thu May 10, 2018 1:16 am

MRHP wrote:
Tue May 08, 2018 4:52 pm
Just making sure that the EL34 / 6CA7 type tube will work in this amp??

Without tube socket changes??

Just bias adjustment only??

Looking at some Mullard xf2 EL34 1965 vintage nos tubes.

SNOOP help a brotha out I got the tube fever and the only cure is more vintage tube smell!!!
6L6/KT-88 are beam tetrode, EL34 are pentode. They =can= be cross compatible but the beam tetrode does not require a ground at pin 1, where the EL34 does. There also may be differences in DC voltage levels. They are probably close enough to go ahead and purchase the tubes you are interested in and make adjustments at CF. My Marshall amp was first designed to run 5881 (6L6) and later was sold with EL34 tubes, but not exactly sure what the change was to the amp for the EL34's to work.

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Re: 2018 Carverfest Tube Power Amplifier Build

Post by MRHP » Fri May 11, 2018 7:30 am

Thanks for the info UncleMeat. =D>

And keep the tranquilizer gun handy Snoop :lol:
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Re: 2018 Carverfest Tube Power Amplifier Build

Post by BarryG » Sat May 12, 2018 8:22 am

I think Kevin (KVE777) would probably be able to tell you how to rewire! He knows a lot about tubes and was encouraging those with tube buffers to roll tubes and use tubes that required slight reworking the wiring!

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Re: 2018 Carverfest Tube Power Amplifier Build

Post by UncleMeat » Sat May 12, 2018 6:16 pm

Or Bob, since he'll be there. He can show you how to set the nominal DC supply voltages so the tubes will be operating correctly.

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Re: 2018 Carverfest Tube Power Amplifier Build

Post by MRHP » Sun May 13, 2018 3:21 pm

Any guess on power output with the EL34's? I have lots of high power amps, with these amps I'm looking for the sweetest sound I can get.

The Vintage EL34's are affordable compared to vintage KT88's or 6550's.
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Re: 2018 Carverfest Tube Power Amplifier Build

Post by fxbill » Tue May 15, 2018 4:29 pm

I wouldn't guess with Bob's new circuity, but normally a pair of EL34s will give you about 30-35 watts....or about 15 in triode mode, but with a very warm and sweet sound!

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Re: 2018 Carverfest Tube Power Amplifier Build

Post by UncleMeat » Tue May 15, 2018 6:01 pm

I'm thinking it might be closer to 50wpc. That's the max rating for 2 EL34 in push-pull, so if Bob's amp/circuit can be optimized for the EL34 it should be close to that. But of course that's a maximum so you're probably looking at 35-45wpc nominal without audible distortion on peaks.

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Re: 2018 Carverfest Tube Power Amplifier Build

Post by MRHP » Wed May 16, 2018 5:56 pm

Cool. Anything in the 25 to 45wpc would be awesome!

Just don't tell anybody I'm looking for lower power...I might get banned from Carverfest. :-$
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Re: 2018 Carverfest Tube Power Amplifier Build

Post by hewlew1 » Wed May 16, 2018 8:01 pm

Blasphemy shame on you mrhp
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Re: 2018 Carverfest Tube Power Amplifier Build

Post by UncleMeat » Fri May 18, 2018 2:44 am

Pentode VS. Beam Tetrode:
http://www.r-type.org/static/tet-pent.htm

Here's a quote that might be of interest from http://www.r-type.org/static/grid14.htm :
RCA did have facilities to successfully translate the design (of the Beam Tetrode) into a working valve. The result was the 6L6. It was more efficient than an equivalent Pentode, due to lower screen dissipation, hapilly it also produced one third less third harmonic distortion. The ear is reasonably tollerant of second harmonic distortion up to about 5% but not third harmonic distortion which must be reduced to very low levels for qood quality sound. The Triode produces inherently lower third harmonic distortion than other valve types. The Pentode produces significant amounts.

Within a few years most manufacturers had introduced Beam Tetrodes for audio output service. Mullard remained loyal to the Pentode. The top honours went to MOV for their KT range, especially the KT66 and later the KT88.

Beam tetrode valves were originally developed for use as audio-frequency output valves, but the principle was also applied to many types of radio-frequency tetrodes both for receiving and transmitting. Their superiority over pentodes for AF output is due to the fact that the distortion is caused mainly by the second harmonic and only very slightly by the third harmonic, which is the converse of the result obtained with a pentode. Two such valves used in push-pull give a relatively large output with small harmonic distortion because the second harmonic tends to cancel out with push-pull connection.

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Re: 2018 Carverfest Tube Power Amplifier Build

Post by MRHP » Sun May 20, 2018 12:08 pm

Uncle Meat am I reading this right. The 6L6 and or KT-88 has a lower 3 harmonic distortion rate compared to the EL34. And the human ear picks upon 3rd harmonic distortion more than any other?


End result I might should be looking for a Beam Tetrode tube instead of the EL34 Pentode type tube?


Thanks for this info as I enjoy reading and learning about tubes and tube amps!
TFM-75 serial #0001
PT-2400 serial #0001
Baby Black Magic serial #0001
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Re: 2018 Carverfest Tube Power Amplifier Build

Post by UncleMeat » Mon May 21, 2018 12:11 am

MRHP wrote:
Sun May 20, 2018 12:08 pm
Uncle Meat am I reading this right. The 6L6 and or KT-88 has a lower 3 harmonic distortion rate compared to the EL34. And the human ear picks upon 3rd harmonic distortion more than any other?

End result I might should be looking for a Beam Tetrode tube instead of the EL34 Pentode type tube?

Thanks for this info as I enjoy reading and learning about tubes and tube amps!
Yes, the 6L6 and KT (kinkless tetrode) tubes inherently have lower 3'rd harmonic distortion than the EL34. I don't know if amp design can reduce 3'rd harmonic distortion or if it will always be higher than 2'nd order distortion in pentode power tubes.

Some people prefer the sound of EL34 tubes to 6L6/KT. There are also amps that use a combination of 6L6GC and EL34 and 'blend' their sound to allow some 3'rd harmonic in. The amps I've seen that do this use 2 pairs of 6L6GC and one pair of EL34. 6L6, 6L6GB, and 6L6GC have different max power ratings, the GC has the highest of the 3 at ~45WPC from a pair in push-pull.

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Re: 2018 Carverfest Tube Power Amplifier Build

Post by sea » Tue May 22, 2018 1:02 pm

Just a quick update. All deposits are in. We have a total of 67 amps committed to 41 different people. 15 in for one amp and the balance in for two. I will list the participants below. Please let me know right away if you spot any discrepancies. The remaining money will be due mid to late July.

I know that some of you are not planning to attend. We do not have any details worked out on packing and shipping. It would be preferable if those participants could find someone who lives close enough by to have them mule it for you.

One Amp
BarryG
HappyTrails
DaveS
AR9Jim
ItchItch
Kingman
Don
OldTexasDog
AngeloD
SteveK
peck555
pindrop
compwaco
dennis47
jldeni

Two Amps
Morris
Nahash (Greg)
RobertR
Magnaryder
Mbkseam
LonerT
kve777
Iamjohngalt
Frenchguy
BrianT
Eddie
sea
Martin1970
Hewlew
Shortcake
Radioeng2
Treitz
Jerry
Dnspy007
BobSmi57
MRHP
Trav0810
Uncle Meat
B-Man
packratt
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Re: 2018 Carverfest Tube Power Amplifier Build

Post by oldtexasdog » Wed May 23, 2018 11:15 am

sea wrote:
Tue May 22, 2018 1:02 pm
Just a quick update. All deposits are in. We have a total of 67 amps committed to 41 different people. 15 in for one amp and the balance in for two. I will list the participants below. Please let me know right away if you spot any discrepancies. The remaining money will be due mid to late July.

I know that some of you are not planning to attend. We do not have any details worked out on packing and shipping. It would be preferable if those participants could find someone who lives close enough by to have them mule it for you.

One Amp
BarryG
HappyTrails
DaveS
AR9Jim
ItchItch
Kingman
Don
OldTexasDog
AngeloD
SteveK
peck555
pindrop
compwaco
dennis47
jldeni

Two Amps
Morris
Nahash (Greg)
RobertR
Magnaryder
Mbkseam
LonerT
kve777
Iamjohngalt
Frenchguy
BrianT
Eddie
sea
Martin1970
Hewlew
Shortcake
Radioeng2
Treitz
Jerry
Dnspy007
BobSmi57
MRHP
Trav0810
Uncle Meat
B-Man
packratt
wrf


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