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Old 7th October 2012, 11:41 PM   #1281
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Hi Ian,

Thanks for your response.
I'm lucky enough to have a pair of custom electraprint transformers I got for a project that never got off the ground. The transformers are 10k, 20w, UL, 6 ohm secondary. I cannot recall the exact frequency response figures but they were something like -3db 7hz and 85khz. Square wave response was very good.

I've managed to pick up five Brimar 6F6G tubes for $16USD and I've got a box full of regular 6V6's that I can try as well.

If your interested, I can provide updates on the build but it will be about 4weeks before some of the parts arrive.

Kind regards
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Old 8th October 2012, 12:20 AM   #1282
6L6 is offline 6L6  United States
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Quote:
Originally Posted by Drewaudio View Post
I cannot recall the exact frequency response figures but they were something like -3db 7hz and 85khz.
That's Jack for you! Incredible response. A friend of mine and I built a EL84 PP amp, and had similar transformers, their measurements were fantastically good, much like yours.

I have a pair of Electra-Print SE transformers, and even with the 100ma DC gap they measure -3db 18hz-60khz.

A few years ago I had the opportunity to visit him at his home/shop. Imagine a mad scientist, and that's basically him. The best transformers come out of a shop in northern Las Vegas... Go figure!


Best of luck with your build, please take and post lots of photos. We would all love to see your progress.
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Old 13th November 2012, 12:51 AM   #1283
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Default A new baby Huey is born...

Hi all,
I thought I'd build a Baby Huey as my first power amp scratch project, I have heard such good things about this amp and it seems that there is plenty of advice, expertise and helpful people on this site.

So far the chassis is done and transformers built and in place. That, I think is the easy part !!

I have made the chassis very compact, after-all it is a BABY Huey.

I've no doubt i will be asking for more advice at some point so I thought it only decent to show off my work so far !

Thanks to all those who have tolerated my limited electronics knowledge until now....! Can't wait to hear her first words.....
Ian. East Sussex UK.
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File Type: jpg BHTUBESCLASH.JPG (464.2 KB, 535 views)

Last edited by sharkey22; 13th November 2012 at 12:54 AM.
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Old 13th November 2012, 01:55 AM   #1284
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Default Nice start...

Thx for the pics. I'll be watching your build. I'm very curious on how the build goes and what it sounds like. But I need to finish one project before starting another..... No hurry but keep it rolling....
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Old 13th November 2012, 03:03 AM   #1285
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Ian (Sharkey22),
Good start, that looks about the ideal size chassis, you would not want to try to build it into anything smaller. Some of my greatest frustrations have come from trying build "stuff" into too small an enclosure.
Cheers,
Ian
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Old 13th November 2012, 05:08 PM   #1286
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Quote:
Originally Posted by gingertube View Post
Ian (Sharkey22),
Good start, that looks about the ideal size chassis, you would not want to try to build it into anything smaller. Some of my greatest frustrations have come from trying build "stuff" into too small an enclosure.
Cheers,
Ian
Hello and thanks for your comments & encouragement. I am building this with pretty much zero tech knowledge following your schematic except for the HV B+ supply. I have a choke from an old Vortexion EL34 push-pull PA amp. I want to keep the PS as simple as possible whilst taking advantage of the choke. The HV on my transformer is 290-0-290 and the resistance of the choke is 125 Ohms. I am not sure of the chokes inductance so am slightly stumped so-far as component values go. I have had a few goes using PSUDII but am slightly confused regarding splitting the power for each channel also I think I may have been aiming for excessively smooth voltage at the expense of current/voltage stability under load...Please could you suggest a suitable and simple "ball-park" schematic for me to follow. I am reluctant to place my components order until I am confident with the PS design.

Regards Ian.
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Old 14th November 2012, 12:26 AM   #1287
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Ian,
Here is a power supply, a bit over the top maybe but adjust to your taste.

Fuses are not absolutely required if you fuse the transformer primary.

The 10nF Class X and 2 x 10R before the rectifier diodes are intended to block any diode switching noise from coupling back through the transformer into other windings (particularly bias supply windings etc.). "Class X" is a safety rating and signifies a capacitor which is suitable for connecting from active to neutral on a mains supply. They will generally be a metalised polypropylene or metalised polyester.

Diodes are anything ultrafast and soft recovery, like UF4007

Diodes have supression caps fitted across them (optional), again to help suppress diode switching noise. Thezse should be 10nF 2kV high voltage ceramics.

C4 can be adjusted to trim the power supply voltage, 10uF will give a little less output voltage, 5uF and lower will give a lot less voltage. This cap has about 250 mA RMS ripple current in it (according to PSUDII). Check the rating of the cap you use (if in doubt use [for example] 2 off 10uF in parallel to give you the 20uF)

The 220K 2W before the choke is a bleed resistor to discharge the capacitors when you turn the power off. Since we are bleeding away current anyway then you might as well put a LED in series with the bleed resistor. Use a front panel mounted Green LED (or BLUE if that rtocks your boat) as a power ON indicator OR use a RED LED under the chassis as a warning that high voltage is ON.

Use a common 100uF/450V after the choke and then use 10R 2W "isolating" resistors in the feed to each channel.

At each channel use a 100uF/450V with a parallel 100nF/630V polypropylene cap connected with their +ve right at the output tranny centre tap feed and their neagtives at the point where the output tube cathode circuits return to 0V.

Cheers,
Ian
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Last edited by gingertube; 14th November 2012 at 12:33 AM.
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Old 14th November 2012, 11:42 AM   #1288
stajo is offline stajo  Sweden
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Hello

I dont want to be a sceptic but I wonder what the purpouse is with all this filtering in a common mode noice cancelling PP configuration? Refered to famous constructions like QII for exemple a simple and small C-R-C for the powertubes is more then enough and gets it completely silence.

The splitter is another thing where "expensive" stuff like chokes etc can do some proper work. In some configurations G2 on the powertubes needs good treatment also but filtering powertube anodes with big chokes etc, where most of the current runs, seems like a bit over the top for me.

What is your opinions?

Edit: I recalled that the original version did not have this filter so maybe I was kicking in open doors and have to wear the silly hat for a while hat but I also recall (I think!?!) that for example Morgan Jones uses chokes for power anode load filtering in his Bevois Valley. IE I was more interested in the subject then critisizing anyone. I have the feeling that big chokes here can cause more pain then good, causing ringings between OPT and choke inductances etc.

Staffan

Last edited by stajo; 14th November 2012 at 12:01 PM.
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Old 14th November 2012, 09:44 PM   #1289
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Staffan,
I did say that the supply was "a bit over the top maybe". Sharkey22 wanted to use the choke so I included it. Having built many amps I find that you may as well put this level of detail in from the start as it is usually messy to try and "shoe horn" extra components in afterwards.
The Baby Huey effectively has only a single power supply rail and so making it as clean as possible is unlikely to be wasted effort, some builders have even used regulated supplies.
Power Supply noise residuals are a source which form intermodulation distortion products with the signal (put a sine wave through the amp, look on a spectrum analyser and see all of the sidebands due to intermodulation with power supply ripple). If the ripple is'nt there or is greatly reduced (or if its harmonic content is greatly reduced) then so will those intermodulation products be reduced.
For Power Supplies I'd rather over design than under design.
Cheers,
Ian
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Old 15th November 2012, 10:02 AM   #1290
stajo is offline stajo  Sweden
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I'm like you Ian. I tend to try and stay on the safe side on PSU filtering rather then the opposite.

On the topic of power anodes in PP config me and a friend did a test not so long a go. The build was a design by David Hafler borrowed from a Dynaco commercial paper http://www.the-planet.org/dynaco/Misc/Transformers.pdf (figure 3). The splitter is a floating paraphrase and GNF is different but on the output side it is close to Baby Huey (EL84 PP UL).

Sitting close to 100+ dB speakers we evaluated different B+ filtering to to the EL84s. We started with Haflers 40-100-40 C-R C but we had a clear hum. We also tried with different chokes instead of the R. The hum slightly reduced but so did the "happyness" in the music. It became duller.

We ended up on 40-100-140. It was completely silent with the ear in the cone and the happyness in the music was still there. Good tubematching and a balanced splitter is necessary for that.

So in filtering for PP anodes nowadays I rather tend to discover what is the absolute minimum for complete silence rather then going for the safe full blown filter.

Slightly OT but we also discovered a big difference on different capacitors here. Our final choice was good quality electrolytes on both C. We tested against big PIOs and polyprop and also cheap electrolytes. The favourite was Evox/Rifa PEG124 33 uF 450 V, 1 on first C and 3 on second added with a 40 uF motorrun on second C. With the ear in the cone in full volume and no signal we heared nothing but the slight breeze from the tubes (i dont know the english expression). Like slow landwash waves a summer night by the ocean.

Just my 2 cents. I dont have any claims for being right in all cases. It was a fun long night with the soldering iron and it gave many surprices.

cheers
Staffan
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