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Old 1st August 2007, 03:36 AM   #291
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Thanks


Thas my earth, and all the aluminum parts are attached to him (screws of the sockets to) , i think it will work fine.

Click the image to open in full size.


The power lines are ready lacked place for the CCS's

Click the image to open in full size.
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Old 1st August 2007, 04:42 AM   #292
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raidprotector,
I am very impressed with your build method.
Keep us informed of your progress.
Best Wishes
Ian (Gingertube)

P.S.
For those who have built a version of this amplifier using current sources in the output tube cathodes with bypass capacitors, here is another experiment for you to try:
Have a look at what Allen Wright did on this amp:

Click the image to open in full size.

Notice that the 0V side of the cathode bypass capacitors do not go directly to 0V. The 2 0V ends of the capacitors are connected together and then have a 68 Ohm resistor to 0V. You can try this on a "Baby Huey". The fact that we use current sources rather than fixed resistors for the cathode biasing will not make any difference to this scheme.

This is a 3rd harmonic distortion suppression scheme and it is worth trying on a "Baby Huey". Try resistor values of between 33 ohms and about 150 ohms (use 2 watt resistors) to see what sounds best. You are listening for a smoother, less "Edgy" sound, particularly at higher frequencies. And of-course, let us know if you think it makes any difference, and if so, what resistor value sounds best to you.
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Old 1st August 2007, 01:45 PM   #293
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Friends,

I eventually got sick of Flickr albums, a very "nice" piece of s...

Now I transfered (and improved) my site to Multiply, much better stuff and user friendly tools, well organized space:

http://vacuumtuberesearch.multiply.com/

Hope surffing there is smoother now...

Thanks all,
Ricardo
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Old 2nd August 2007, 01:58 AM   #294
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Thank you gingertube... its very good to me read that.

I will
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Old 15th October 2007, 04:57 AM   #295
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Default Allen Wright's 3rd harmonic suppressor...

Ian -

Have you tried this method with the EL84 Huey? If so, what were your results and resistor value?

Adam
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Old 15th October 2007, 05:10 AM   #296
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Adam,
Not yet - too many projects and not enough time.
I had a couple of JADIS JA80 Monoblocks (80W Class A using 4 KT88 in each channel) and an 845 SET turn up for repair, a guitar amp to mod for cleaner sound and a guitar amp to design and build for a friend and a new EL84 Baby Huey half constructed as monoblocks but fixed bias this time so the mod is not applicable.

Starting to get a name around the local scene for being able to build/fix/modify amps and am having trouble saying NO - doesn't help that the local tube supplier keeps sending people to me, so my own projects are on hold till I can "clear the decks". I'll have to practice saying NO.

Hope to get back to the original EL84 Baby Huey to try this mod soon.

Cheers,
Ian
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Old 15th October 2007, 04:26 PM   #297
dupyv is offline dupyv  Luxembourg
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Default Ring-of-Two current source on Baby Huey

Ian,

I'm in the building process of a Baby Huey amp.
While breadbording and testing the ring-of-two current source of the EL84's, i noticed that they
don't have an auxiliary reference 12V-supply as usual, but the 5k6 resistor is connected to the collector of the MJE340 instead.

This makes a CCS that isn't spot-on the 38mA per EL84, but varies +/-4 mA depending on the voltage the CCS is exposed to on the EL84's cathode.
Is there any further thought behind that besides simplicity (=saving a reference supply) ?
My implementation gives the EL84 Bias-Blocks an auxiliary reference supply with a TL317.

As soon as my Baby-Huey is finished I'll report back (I'm progressing slowly due to lack of time).
Thanks for sharing your great work Ian.

Kind regards,

Yves
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Old 15th October 2007, 11:52 PM   #298
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Yves,

I think you probably meant 4mA total variation, that is +/- 2mA as the applied voltage swings say 12 volts either side of the 12V DC level (which is the nominal bias voltage for the EL84).

In practice the cathode bypass cap will hold the voltage the CCS is exposed to at the EL84 cathode at a reasonably constant DC level (at the bias level) as the AC component will be shunted around the CCS by the bypass cap.

Taking that 5K6 back to an auxilliary +12V or similar supply, rather than to the cathode will certainly be an advantage if implementing the bypass cap modification suggested in a post above, because then the CCS could be considered to not be fully bypassed and some AC residual will appear across the CCS.

Thanks for raising this - it is worth having a think about.

Cheers,
Ian
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Old 18th October 2007, 02:22 AM   #299
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Default Finally building this amp...

I've been experimenting with EL84 amps and am finally building a Baby Huey.

I'm using Dynaclone Z-565 OPT's. I have a Hammond 372JX - 300V@250mA which will push the voltage well above what is desired. Is it merely a matter of tweaking with higher value (and higher W rated) power resistors than the 47R's in the schematic or would there be a more suitabe method of dropping the HT? I have a few good chokes to choose from if necessary.

Best,

Adam
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Old 18th October 2007, 03:21 AM   #300
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Adam,
Those 47R 2W in the original schematic were subsequently dropped to 4R7.
Its not a great idea to waste heat and power in dropping resistors in the main HT supplies.

Download PSUD2 from Duncan Amps Webpages and do some power supply modelling.

Ideal Voltage is about +320V. You really don't want to go above say +350V and even then I would change the 16 Ohm resistors in the EL84 cathode current sources to 18 Ohm to knock the idle current back from 38mA per tube to about 34 mA so as to keep total dissipation in the EL84s to around 12 watts.

Choke Input is a really good way to go as you can fine tune the final output voltage with a 0.5 to 2uF cap straight off the rectifier and before the choke. PSUD2 models this behaviour quite well. If you have seriously too much voltage you may like to even think about a tube rectifier although it may look a bit weird with a thumping great rectifier tube adjacent those little 9 pin tubes. 5AR4 would be the go.

I have 6V6 version of the Baby Huey running with a transformer similar to the 372 you quote. In that I use a 5R4 into 2uF polypropylene followed by a 8H 150mA choke for each channel and about 200uF of cap after each choke. (Actually I have 100uF electrolytic, 60uF polypropylene and 1 uF polypropylene all in parallel - so its about 160uF).

I also have an earlier version of the 6V6 which has a solid state rectifier into 2uF then a 2H 200mA choke followed by 100uF electrolytic. That then splits to the 2 channels each with 4R7 and 60uF polypropylene as the HT feed.

The tube rectified version with separate chokes feeding each channel perhaps sounds maybe 1% better.

If you go the SS rectifier direction that means that you can voltage double the 5V winding to generate the negative supply to return the front end diffamp current source to. That could also be generated using the bias tap on the HV winding.

Plenty of ways to skin a cat.

Cheers,
Ian
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