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45 amp build direct coupled
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Old 24th March 2018, 02:00 PM   #21
faithintruth is offline faithintruth  Canada
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Hi mbrennawa...awesome website and writing!
Do you use the parallel 300B? Which pre-amp?

Really great...I'll be reading more!
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Old 24th March 2018, 02:20 PM   #22
euro21 is offline euro21  Hungary
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45 amp build direct coupled
Quote:
Originally Posted by faithintruth View Post
Draw me the gyrator
Voilá.

BTW Ale' site http://www.bartola.co.uk/valves/ is good starting point to understand "gyrator"'s operation.
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Old 24th March 2018, 03:14 PM   #23
euro21 is offline euro21  Hungary
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Quote:
Originally Posted by soulmerchant View Post
E180F, E280F and 7788 should all be up to the task and are a little more obtainable these days.
Is "obtainable" the most important aspect in our hobby? :-)
BTW I'm a collector of graphite anode 801. :-)

I use both of these tubes, but in the right place.

D3a an E280F (as CCS loaded VAS) is interchangeable in my 300B amplifier, but have a little different character (I have several tubes of them, from several manufacturer).
D3a is the "rock", E280F is "sophisticated".

E180F/6688 is a little "weak" in this operating point, and E810F/7788 is a little "boring".
E810F is very good tube (for example in phono), but "hate" large swing, distortion (H3) is very quickly increasing.

As you can see in Pete Millett's site High Gm driver pentodes , among them the D3a is the most "better" (Gm, swing, THD) for using as two stage amplifier VAS stage.
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Old 24th March 2018, 03:41 PM   #24
RajkoM is offline RajkoM  Bosnia and Herzegovina
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E180F / 6688 is a little "weak" ...

Yes.
The E180F is a little preambitious tube. From data sheet the max dissipation is 4W (Pa + Pg2) ... that is too much for this little-glass tube.
In old broadcast repeaters, the E180F was the most "short of life" tube.

Btw, E180F is a great tube for us DIYers, but dissipation should not exceed 2W.
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Old 24th March 2018, 06:17 PM   #25
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by faithintruth View Post
Hi mbrennawa...awesome website and writing!
Do you use the parallel 300B? Which pre-amp?

Really great...I'll be reading more!
Thanks. The 300B went away to play music for someone else :-)
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Old 24th March 2018, 09:53 PM   #26
soulmerchant is offline soulmerchant  Switzerland
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Quote:
Originally Posted by RajkoM View Post
E180F / 6688 is a little "weak" ...

Yes.
The E180F is a little preambitious tube. From data sheet the max dissipation is 4W (Pa + Pg2) ... that is too much for this little-glass tube.
In old broadcast repeaters, the E180F was the most "short of life" tube.

Btw, E180F is a great tube for us DIYers, but dissipation should not exceed 2W.

Regarding the E180F, The Mullard datasheet notes the pa max. at 3 watts. That is obvious for a small envelope. I have had no problem running the Tesla gold pin ones at about 2.3 watts. I find 175V on the plate biased for 13mA to be pretty nice. mu is almost 50, just like on the datasheet. Also nice is that they are pretty consistent (unlike so many soviet valves). Ok, once in a while you do get a dud, but they are not that often, and for the price, I just can't slag this little guy. Short life? like 2'000 hrs... I wish china 2a3's would last that long.... Also, I find that it is one of the most forgiving of all the UHF pentodes when triode strapped. On super cheap builds, with garbage iron it simply shines...

But, unless you are a true hobbyist, please don't buy this tube. its crap. honest. It seriously sounds like total garbage. Ignore what I wrote above. It breaks if you drop it. It's made of glass. Don't touch it with a barge pole. it should be only sold in large lots on the cheap to foolish buyers (like me)
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Last edited by soulmerchant; 24th March 2018 at 10:01 PM.
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Old 24th March 2018, 10:03 PM   #27
Bigun is offline Bigun  Canada
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45 amp build direct coupled
Maybe try 6E5P, when triode wired it's superbly linear and one of the favourites of our Russian DIY hobbyists.
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Old 24th March 2018, 10:14 PM   #28
soulmerchant is offline soulmerchant  Switzerland
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Quote:
Originally Posted by euro21 View Post
Is "obtainable" the most important aspect in our hobby? :-)
BTW I'm a collector of graphite anode 801. :-)

I use both of these tubes, but in the right place.

D3a an E280F (as CCS loaded VAS) is interchangeable in my 300B amplifier, but have a little different character (I have several tubes of them, from several manufacturer).
D3a is the "rock", E280F is "sophisticated".

E180F/6688 is a little "weak" in this operating point, and E810F/7788 is a little "boring".
E810F is very good tube (for example in phono), but "hate" large swing, distortion (H3) is very quickly increasing.

As you can see in Pete Millett's site High Gm driver pentodes , among them the D3a is the most "better" (Gm, swing, THD) for using as two stage amplifier VAS stage.
Maybe its taste, but I prefer the E280F to the D3a when driving 2a3 or 45. The E180F does surprisingly decent job as well though. It is true that the E810F needs some care in implementation.
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Last edited by soulmerchant; 24th March 2018 at 10:17 PM.
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Old 24th March 2018, 10:19 PM   #29
soulmerchant is offline soulmerchant  Switzerland
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Quote:
Originally Posted by Bigun View Post
Maybe try 6E5P, when triode wired it's superbly linear and one of the favourites of our Russian DIY hobbyists.
I heard it a while back at a friend's, and it is indeed impressive! Nice price too, but make sure to buy a bunch to find a pair that have a similar gm.
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Old 25th March 2018, 12:21 AM   #30
TonyTecson is offline TonyTecson  Philippines
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45 amp build direct coupled
Hi, there are some nice IXYS depletion mosfets that can be deployed as CCS cathode biasing,PartDetail
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