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Old 3rd August 2004, 10:51 PM   #11
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Damn. The .047 coupling cap should read 1uF. Later.
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Old 4th August 2004, 06:32 AM   #12
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Couple things:
First of all, this schematic appeals to my minimalist philosophy and I'm loving the way this looks (what's the power output?). Yes, I would like to see your PS ideas for this guy; (I definately want to use the 5u4 though.) I don't like chokes, nor do I have room for one an the chassis- so that may or may not be a problem. I'm also thinking about filament regulation with an lm350. BTW, would I add the attenuator before the 100k?? I'm assuming that the screen grid (labeled "to B+") is wired directly to 250 volts. Lastly, the OPT's are definately rated @ 5k with 8 and 4 ohm taps, not 4.8k like the schematic details.

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Old 4th August 2004, 07:33 AM   #13
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Hi cadaverdog

If you want to experiment other kind of circuits - with other voltage amplifing tube - you may give the 12AX7 or 7025 (can be used instead of 12AX7wa, having even better specs) a try. There are lots of schematics available for this combination of tubes. You can even search for schematics using the ECL86, which is a EL84 and half a 12AX7.

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Old 4th August 2004, 03:38 PM   #14
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Quote:
Originally posted by cadaverdog
Couple things:
First of all, this schematic appeals to my minimalist philosophy and I'm loving the way this looks (what's the power output?). Yes, I would like to see your PS ideas for this guy; (I definately want to use the 5u4 though.) I don't like chokes, nor do I have room for one an the chassis- so that may or may not be a problem. I'm also thinking about filament regulation with an lm350. BTW, would I add the attenuator before the 100k?? I'm assuming that the screen grid (labeled "to B+") is wired directly to 250 volts. Lastly, the OPT's are definately rated @ 5k with 8 and 4 ohm taps, not 4.8k like the schematic details.

Thanks!!
Basically the schematic is a Decware Zen using a 5687 in the gain stage instead of a 6N1P. The output power is about 3 watts. I didn't use a choke in the power supply of this amp so that won't be a problem. The attenuator would take the place of the 100K resistor. I had no problems with hum but if you want to go DC on the filaments I would start out with just a filtered DC supply. Keep the first project simple. Basically I need for you to measure the no load voltage on your power transformer from one lead to the center tap and then measure the winding resistance from one lead to the center tap and I can tweak the power supply to fit your transformer. The layout of the amp I built can be found here:

https://athena.safe-order.net/decware/zkit02.htm

Some of the values are different but that is essentially the amp I built.
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Old 4th August 2004, 05:03 PM   #15
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After downloading the schematic from Decware, I would have to say that this is definately the way to go. Everything I want is there and I could put all of it on my chassis with little or no modification. I did some measurements on my PT and came up with the following:
Filament 1: 7.25V .2 ohms
Filament 2: 5.65V .3 ohms
High Volt : 366V-0-366V 63.5 ohms (R-from one lead to CT)

There are no center-taps on the filaments, and judging by the Decware schematic- that might be a problem. Also, the 01uf coupling cap seems a little small (add a 1uf?) What do you think?
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Old 4th August 2004, 10:01 PM   #16
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Quote:
Originally posted by cadaverdog
After downloading the schematic from Decware, I would have to say that this is definately the way to go. Everything I want is there and I could put all of it on my chassis with little or no modification. I did some measurements on my PT and came up with the following:
Filament 1: 7.25V .2 ohms
Filament 2: 5.65V .3 ohms
High Volt : 366V-0-366V 63.5 ohms (R-from one lead to CT)

There are no center-taps on the filaments, and judging by the Decware schematic- that might be a problem. Also, the 01uf coupling cap seems a little small (add a 1uf?) What do you think?
Well you can see the finished product for yourself below. No CT on the filament winding is not a problem. Especially if you are going to be using a regulated DC supply for the filaments. Yes the .1 cap is too small. Use a 1uF 600v cap. I will post the PSU in a few minutes.
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File Type: gif cadaverdog's se el84 (small).gif (12.4 KB, 112 views)
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Old 4th August 2004, 10:15 PM   #17
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Here is the PSU. Keep in mind that the first resistor (R1) is dropping a lot of voltage. Make sure to use a 25 watt wirewound resistor. Michael Percy Audio is a good place for the 25 watt ww and for Mill's 12 and 5 watt wirewounds. That is pretty much all I use in power supplies for power amps. He also sells Kiwame carbon film resistors that work very well in tube amps as plate and cathode resistors. The choice is yours.
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File Type: gif cadaverdog's se el84 psu (small).gif (11.3 KB, 108 views)
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Old 4th August 2004, 10:47 PM   #18
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Hi,

Any particular reason why the cathode resistors of the 6BQ5s are shared between channels?

Cheers,
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Old 4th August 2004, 11:04 PM   #19
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Hi,

Quote:
Damn. The .047 coupling cap should read 1uF. Later.
1µF into 470K?
0.220µF would already be much more low frequency than the OPT can pass.

Don't get me wrong, it will of course work but the higher the RC constant the slower the cap will be.
This could be something worth fiddling a little with. You may find the amp's transient improve with smaller value coupling caps, moreover I'd doubt you'd notice any difference in the bass response.

Cheers,
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Old 4th August 2004, 11:23 PM   #20
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Quote:
Originally posted by fdegrove
Hi,

Any particular reason why the cathode resistors of the 6BQ5s are shared between channels?

Cheers,
Hi Frank,

No. Other than when I was building this amp the schematic model I used biased the output tubes this way. I have since built a different amp and used separate cathode resistors. You are correct in pointing that out. Separate resistors would probably be preferable. If you do use separate cathode resistors CadaverDog you should double the value to 300 ohms for each resistor as yo will only have half of the current flowing through the resistor and therefore only half of the desired voltage drop (10.5v - 11v).
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