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 NEW  Bruce Heran outlines the details and construction of his simple DIY 6DJ8 (ECC88) Tube Hi-Fi Headphone Amplifier Project.

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PostPosted: 25 Feb 2011, 10:28 
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I think there are too many people reading old textbooks where MV's were typically used in the PSU of transmitters . For voltages in audio equipment these issues can be relaxed somewhat , although I do heat the fils for a minute before power on and give a good heating-through for 15 mins at first power up or if the equipment is moved . It's easy to tell when the mercury condensing on the inside of the envelope is satisfactory and it's time to hit the B+ switch . It's also easy to connect the 83 with a pair of damper diodes in a bridge rectifier or '!@#$%^&' bridge and completely avoid the B+ switching issue altogether . Type 83 are fairly rugged and can take a cap-input supply , in fact I find these a lot easier to use then 866A or the Britsh RG1-250A globes .

1mH or less plate suppressors kill the RFI as do CM chokes at the filament pins...

A very nice sounding rectifier indeed...

Admittedly , not one for newbies though...

BDA


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PostPosted: 21 Apr 2011, 11:06 
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I've added the 5Y3 to the comparison charts. Talk about a saggy tube. No wonder the old Fender "Deluxe" amp sounded so funky when you pushed it hard. It had a major B+ falloff.

If I get the chance, I'll add the 5R4GB and the 5AU4A maybe later this week.
Attachment:
20110421_Tube_Drop.png

Attachment:
20110421_Tube_Drop2.png

As always, comments and questions are more than welcome.


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PostPosted: 07 Jun 2011, 22:02 
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If you'll all indulge me, I have one more post for this thread. And I cannot fathom why I did not see this sooner.

Back when I first posted my calculated log-log plot, I asked the question about what was to be learned from the parallel tube characteristics when plotted against log-log scales. The answer is that all vacuum tube rectifiers operate in a space charge limited state of operation and obey the Child-Langmuir Law (more commonly called Child's Law). The consequence is that all vacuum tube rectifiers follow an I=k*V^(3/2) power law and all exponential power law relations are straight lines on log-log plots. Duh!

The important part of this is that ANY vacuum tube power rectifier V-I characteristic can be plotted from one point on the published I-V characteristic. I was doing it the hard way. (Imagine me pouring over data sheets and reading hundreds of numbers off of plots. :bawling: )

The process is actually simple. First take a single I-V data pair off the published characteristic (call these number Ir and Vr). From this generate a tube dependent constant (k) given by the following relation k=Ir/(Vr^1.5). Then the peak voltage drop at any given peak current for that tube is simply V=(I/k)^(1/1.5). When I checked the results given this way against the numbers I had read off the published plots, the errors were on the order of +/- 1%. This Actually Works! :thumbsup:

Here are my latest plots comparing all the common rectifiers I could find. These are all full wave rectifiers except the 35W4 which is shown with a dotted line.
Attachment:
Tube Drop 1.png

Attachment:
Tube Drop 2.png

Is this useful to anyone?


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PostPosted: 07 Jun 2011, 22:14 
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Yes, very useful. Thank you! :D

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PostPosted: 07 Jun 2011, 22:29 
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Log is great for making straight line plots! ;)

Yes, this is extremely useful information. Thank you for sharing it. If you would like to summarize your results, I could find a spot on the main site for this info.

BTW - there is a small typo. GZ43 should be GZ34.

Cheers

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PostPosted: 10 Jul 2011, 21:33 
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I've been listening to my 6V6 "Lacewood" amp and I've noticed a funny behavior from my Electro-Harmonics 5U4GB. When ever I turn the amp on, the 5U4 has a light buzzing sound (it's relatively faint) for about two minutes. After that it quiets down.

I've tried several other 5U4s I have and none exhibit this behavior. As this is the first EH 5U4 I've used, I was wondering if this is typical of the tube or if I just happened to get a noisy one.

Anyone out there share this experience? :?:

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PostPosted: 11 Jul 2011, 06:36 
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I had a vintage RCA 5U4GB in an HH Scott 99-D that buzzed for a few minutes after powering up, then stopped. I have about a dozen others I've tried and none have this "problem".

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Greg


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PostPosted: 11 Jul 2011, 14:31 
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Hi.
Suncalc wrote:
When ever I turn the amp on, the 5U4 has a light buzzing sound (it's relatively faint) for about two minutes. After that it quiets down.
I was wondering if this is typical of the tube or if I just happened to get a noisy one?

Yup. This was a bad tube.

I had the same experience. When the 5AR4 of my ST-70 was going after a pretty long service, the amp buzzed a short while whenever switched on & then quieted down. Once the tube was replaced, no more buzzing.

c-J

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PostPosted: 11 Jul 2011, 16:35 
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Bluesman wrote:
I had a vintage RCA 5U4GB in an HH Scott 99-D that buzzed for a few minutes after powering up, then stopped. I have about a dozen others I've tried and none have this "problem".

It's a directly-heated tube and is probably due to the tension of the filament hangers while cold at switch on . Weather or not this can be classed as a 'fault' is another matter

BDA


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PostPosted: 11 Jul 2011, 21:21 
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Well, I replaced the new Electro Harmonics 5U4GB with an ancient Raytheon 5U4GB and not only did the buzz go away, but I think (after listening to it for a few hours) that it opened up the low end as well.

I need to look for a resonance in the PS filter which could explain a low frequency dependance on rectifier characteristics. It must be a self generated intermodulation product in the filter itself. I guess this is what I get for using two chokes of different values in the filter. :(

I guess it's time permanently relegate the EH 5U4GB to the prototyping pile. Anybody have any experience with the new JJ 5U4GBs? I can't rely on old tubes forever.

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