Bottleneck Push-Pull Salvage Amplifier Competition

[roscoe primrose]

Is anybody other than myself actually building anything?

Yeah, I'm planning to bring at least one

I'm hoping to fire up one of my amps tomorrow.

ray

Guess you're planning on more than one entry as well....

Roscoe

[debk]

As I said before I can't make it unfortunately.  However I still am building an amp.  Should be done this weekend or next weekend.  I will send in documentation for the fun of it.  Wish I could attend, the last one I attended was a blast!

[RayP]

That's great that you are building a couple of amps, Roscoe.  Could you bring along the amp you showed at the last meet as well. It should provide a good benchmark for the others.

And Deb, it's a pity you can't make it. We will look forward to reading about your amp.

I've just applied DC to the filaments of the driver tube of one of my amps. It's an ugly beast and keeps growing like Topsy.

ray

[RayP]

Just a reminder that the meet is a week from today.

ray

[RayP]

For those of you who are planning to turn up on Saturday, could you respond to let us know how many attendees we will have. If you are bringing an entry, could you mention it. It's fine if you aren't bringing anything other than your charming personality.

I'm still struggling with my amps. As usual, I made them too complicated and one of them has been really tough to fit into its receiver box. Even if they don't work, I'll bring them along for you all to gaze at in rapt admiration.

Still, I've got two days.

ray

[roscoe primrose]

One of mine I haven't gotten any further than removing the old stuff from the chassis...  I expect it to be ready for Sat.

Roscoe

[castlesteve]

If people haven't built an amp for the competition then your welcome to bring whatever you want. Can somebody bring a linestage as I don't have a functioning one at present. We will start at the usual time around 9.00ish and go on until you've all had enough.

[dbishopbliss]

I have my linestage from the Russian Tube competition and a Foreplay III.  The Foreplay has stepped attenuators so it may be challenging to get the levels of the amplifiers exactly the same.

In case we need amps, I will bring a Dyanaco ST70 that I have been planning on rebuilding. 

I also have a ST30 variant that I sort of got working.  The circuit is built on a DIYTUBE board, but the circuit was designed for me by Eddie Vaughn using 12AV7 drivers.  The reason I say, "sort of got working" is that the amp seemed to work fine when it was plugged into a preamp I had that was not grounded (a solid state ADCOM).  However, as soon as I plugged it into my Foreplay III it would blow fuses when it was turned on.  I could never figure out what the issue was.  I suspect it has to do with the power supply and some sort of power spike.  Maybe I will bring that along as well and let people take a look.

Edit: I meant to say 12AV7 drivers, not 12AU7

[davechen]

Unfortunately I'm under the weather and will not be able to make it.  Too bad, since, after my visit to Bottlehead HQ, my BeePre is up and working great.

Maybe next time I'll have a Bottlehead DAC to show.

[T Ben]

I will be attending, I can bring the pre-amp, Smack, headphones (same as last time) and I have a interesting tube dac to bring.  I will bring the some headphones.   Last time Dave mention some other headphones he had that sounded nice and would make a great comparison, if anyone has Crack that would round this out.  I will leave the cardboard speakers at home (unless you want me to bring them), I have a much different pair I will try to get up an running for tomorrow, although it needs a sub.   PS, are we meeting at the usual place in Sterling?   Thanks Tony

[castlesteve]

This was an excellent meet. Most enjoyable with great music and good company. I will let ray fill in on what transpired but I just had a good time with old friends doing what I like to do. Let's do it again in the new year!

[RayP]

We had a great time and we are thinking of scheduling another meet in January depending on the weather.

Link to blog of photos here.

ray

[roscoe primrose]

Steve, thanks for hosting, and Ray, thanks for setting this up...

The smoke event in the WE clone amp was due to a shorted 5881, have to call the vendor about that Monday.  Amp is fully repaired already, only one resistor needed replacing.

As far as the new amp, Ray, you're more than welcome to post the values.  Please make the changes mentioned below before posting... A couple of comments based on some more measurements I took this AM.

• C4 & C5 should probably be upped to 250v types, as the voltage can be higher than 190V depending on how the output tubes bias up.  The value probably would be fine at anything at or over 220uF (the values in your junk box are always the best ones to use, right?).
• The power supply turns out to be much higher than I thought, at about 500Vdc.  That runs the dissipation up to higher than 6L6/5881 limits, so I'd recommend either building with a B+ at more like 420-450Vdc, or running 6550 output tubes (which bias up just fine, tried it this AM).
• Old Jolida amps don't cost all that much, especially if you can find one that needs work, and they make a good base platform w/o the need to do metal work, but keep in mind that you're pretty much stuck with a nearly 500Vdc B+ if you go that route, unless you do some serious work on the power supply filtering.

Roscoe

[dbishopbliss]

I will make a point of rebuilding the ST70 for the next meet.  I have the boards so it really shouldn't take too much time.  I just have trouble balancing all my hobbies.  There's a guy offering luthier classes locally.  Must resist, must resist, not enough time.

[dbishopbliss]

Just sent Roscoe a PM about using zeners to triode strap the power tubes in his amp.  Leaving a message here in case he doesn't check his PM's.