Looking for some build advice

[JPeitzman]

Hello everyone!
I have been here for a while, learning, dishing out help when I can, but I haven't done much building with tubes. I have built some solid state designs, currently using a JLH (original 1969 version) and a bread-boarded First Watt B1, been in the bread-board for a while, yes I am lazy. When I need a tube fix I have a Knight EL84 integrated and an RCA theater monitor amplifier (mono for that old school feel). I know that these threads don't always generate the most interest, but I need some advice. Thanks in part to a thread a little while back in the fullrange forum, I have decided to build a pair of CHR-70 MicroTowers for my new apartment. I am looking for a tube power amplifier to pair with them.

I think I have come down to a couple of different designs, but was looking for some feed back on them to see what the experts thought. I am thinking I need something in the 10 to 15 watt range due the sensitivity of the drivers being used. I would love to build a PP-1C, but it just isn't in the budget right now. I am leaning towards a fixed bias Baby Huey. It seem that it would satisfy the drive requirement and has gotten pretty good reports. The other design I am considering is a KT88 (or maybe EL34) SIPP (OddWatt). I don't know much about the OddWatt's, but they too seem to get fairly good reviews. If I went the SIPP route I would not build it as a stereo amp (no monoblocks... probably) and I would change the power supply side a bit.

Now I leave it up to you because I am torn, do I build the Huey, the SIPP, or something else altogether. If something else then I am trying to stay around or under $500, which isn't really a problem with either since I have pretty much everything but iron, and KT88's in the case of the OddWatt.
Thanks and
James

[JPeitzman]

Just for reference...

[Globulator]

Originally Posted by JPeitzman

I have pretty much everything but iron, and KT88's in the case of the OddWatt.

I'm not an expert at all - but have you considered using the GU50 instead of KT88s?

[SY]

I would take the BH over the OddWatt without question. MUCH better design.

You might also consider Pete Millett's Engineer's Amplifier.

[JPeitzman]

Globulator,
I have given some serious consideration to using GU50's for something. They are tough to beat at under $4.00 each for a great tube. I don't know though that I will be using them for this project, but I think I will pick some up anyways.

Sy,
Thanks SY, only two responses, but it seems it will be the Baby Huey since I was leaning that way to begin with. I will however have to look into Mr. Millett's design. Just out of curiosity, I wonder if I should add your RLD to the short list. It seems like it would meet my requirements, and it seems it would be simpler to build than the BH.

Also wondering, what do some think it would take to improve the OddWatt, or is SIPP just not the greatest way to go?

[JPeitzman]

I ended up reading through the entire write up by SY on the RLD today. Very interesting stuff I must say. I actually think I am going to build the RLD instead of the Baby Huey. It seems that it meets or exceeds my speaker driving requirements. It seems to have gotten favorable reviews from it's builders. As an added bonus it would be quite a bit easier to build, or so I feel. Also, the majority of the parts already reside in my basement, just a matter of scraping them all together.

The only thing it seems I am having trouble finding are the 133k plate resistors rated for 2 watts or higher. I don't have much lying around that is rated higher than 1/2 watt, so I am shopping for those. I have only checked Mouser so far, but they don't have much, any suggestions?



for reference...

[Arnulf]

Originally Posted by JPeitzman

The only thing it seems I am having trouble finding are the 133k plate resistors rated for 2 watts or higher. I don't have much lying around that is rated higher than 1/2 watt, so I am shopping for those. I have only checked Mouser so far, but they don't have much, any suggestions?

130K is a standard E24 value and will work just fine. If you can't find one in 2W version, use multiple resistors in series or parallel to get in the neighbourhood of your target.

[JPeitzman]

If 130k will do just fine then I will go ahead and roll with that, thanks!

[Arnulf]

First of all, your tube is likely to differ from datasheet charts that the schematic was mostlikely based upon by far more than 2% (which is difference between 133K and 130K)

Second, E24 scale resistors have 5% tolerance so you might actually end up with 133K resistor when buying 130K.

This isn't an oscillator or similarly critical part so you needn't worry about slight differences.