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Old 9th February 2018, 12:48 AM   #8211
qiuchun63 is offline qiuchun63  China
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M O D ? ? ? - ???? - ????
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Old 9th February 2018, 05:12 AM   #8212
dch53 is offline dch53  Australia
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Quote:
Originally Posted by jayfree View Post
This is the improved Push-Pull Mullard EL34 tube amplifier circuit. The original uses the Dynaco A420 audio output transformers which have a primary impedance of 6600 ohms. The schematic is from the Dynaco Super Fidelity Output Transformers catalog. Obviously I didn't use Dynacos, and I used bigger caps in the power supply. My first tube amp, and I am very happy with it. Time to build another amp, now I have the confidence to do it.
Beautiful! Work of art!
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Old 10th February 2018, 02:10 PM   #8213
hpeter is offline hpeter  Slovakia
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Quote:
Originally Posted by ChrisP View Post
A Beovis Valley.
I was hoping to swap between PCL86 and EL84, so the output transformers are 10k a-a and I can drop a GZ34 in place of the 1st smoothing cap to drop the HT. The voltage was still too high for a PCL86 though so I've had to go for the EL84s. The HT transformer is just a 1:1 isolation transformer. LM317's as ccs set to 40mA in place of the cathode resistor. Toroidy output transformers mounted upside-down.
can you comment a bit more ?
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Old 10th February 2018, 03:50 PM   #8214
ChrisP is offline ChrisP  United Kingdom
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The toroidyís? Well the cables tend to exit the toroidy's straight up, so I was expecting to have to cover them with some kind of shroud until I realised If I flipped them upside-down and cut a couple of holes in the panel where the cables exit the trannies then I can route the cables neatly into the chassis.

Iíve used rubber grommets and had to cut a grommet-sized hole in the transformers rubber mount to keep it neat. It works quite well.

This is an older pic with the pcl86ís still in place. This has a 50V toroidal transformer with a two transistor regulator providing 67.2V for the series heater chain (4xPCL86 & 2xPCC88). Since swapping to EL84ís Iíve switched to AC heating.

It's a great sounding amp. I was running an SE 45 but this EL84 amp has a much flatter response with my BC Acoustique Niger loudspeakers. Horses for courses I guesss?
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Old 11th February 2018, 02:16 AM   #8215
gabdx is offline gabdx  Canada
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Quite heroic wire twisting there, not to mention the gray rectangual caps. El94 is still too forgiving for my taste.
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Old 11th February 2018, 09:43 PM   #8216
raybies is offline raybies  Australia
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Some tube glow...

Click the image to open in full size.

Anyone know how I can get a tube with more blue glow, the left side doesn't glow, the right almost has an infinity symbol ∞?
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Old 12th February 2018, 12:21 AM   #8217
mkane77g is offline mkane77g  United States
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Turn up the heat
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Old 12th February 2018, 03:14 AM   #8218
raybies is offline raybies  Australia
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Quote:
Originally Posted by mkane77g View Post
Turn up the heat
Uuuuhhh, that's some nice glow.

My tubes are already hitting ~240c (~440F) and heating the room; it's summer here... how hot do they need to go?

Click the image to open in full size.
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Old 16th February 2018, 01:09 AM   #8219
Danner is offline Danner
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Quote:
Originally Posted by jayfree View Post
This is the improved Push-Pull Mullard EL34 tube amplifier circuit. The original uses the Dynaco A420 audio output transformers which have a primary impedance of 6600 ohms. The schematic is from the Dynaco Super Fidelity Output Transformers catalog. Obviously I didn't use Dynacos, and I used bigger caps in the power supply. My first tube amp, and I am very happy with it. Time to build another amp, now I have the confidence to do it.
Fine business right there.
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Old 17th February 2018, 11:02 AM   #8220
Profi is offline Profi  Russian Federation
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One of my project 6p36s:
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