• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

The Red Light District - another PP EL84 amp

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#285
I suspect the day after St. Patrick's, not everything in Ireland is being done to 0.0001%.

Yes, the James unit I used was the 6228HS. There is a US distributor, but they don't carry it. I ordered direct from James in Taiwan, paying by wire transfer; the process was smooth and, using "surface" shipping, I got the iron in about 3 weeks. I have nothing but good to say about that company and their products.

Re: voltages, using a 24-0-24 unit, you can try both 24 and 48V for the boost. 48V may be too high, so the center-tap will be your friend.

Having done extensive research into this, I can assure you that the conversion factor is 2 RCH = 1 BCH.
 
#286
Having done extensive research into this, I can assure you that the conversion factor is 2 RCH = 1 BCH.
Click to expand...

In order for this measurement to be even remotely scientific, both units would need to be present simultaneously for the comparison to be valid. My experience is that this can be an unstable environment.

The BCH has a fairly high standard deviation, therefore a relatively large sample size is needed to determine the true mean. Further research is needed.

The SWAG is usually closer then a WAG, which is about the same as a guestimate. All of these is usually "close enough for goverment work". Any of these methods will usually get you to the answer sooner than "Turn it up till it explodes - then back up just a little." For those following the adjustable load thread, you know that that doesn't always work either.
 
#287
In order for this measurement to be even remotely scientific, both units would need to be present simultaneously for the comparison to be valid. My experience is that this can be an unstable environment.
Click to expand...

Mrs. Y (a redhead) did not react well to that suggestion. But she has a much more limited view of science and self-sacrifice than either you or me.
 
#289
SY said:
Yes, the James unit I used was the 6228HS. There is a US distributor, but they don't carry it. I ordered direct from James in Taiwan, paying by wire transfer; the process was smooth and, using "surface" shipping, I got the iron in about 3 weeks. I have nothing but good to say about that company and their products.
Click to expand...
I was planning to get this same transformer and since my experience with THL Audio is positive, I have confidence on the company. I paid by credit card with 2% surcharge :xeye: and had it delivered via EMS. Got the notice I about 1 week and I had to "rescue" it from local customs.

Mr. Chang quoted me NT$5,600 for a pair of 6228HS.
 
#292
That's not too far off from what I paid, if anything it might be a bit cheaper. Last night, I was playing with the compensation in one of the James-based amps here and was very pleased to see that I had to suppress a bit of overshoot on square waves at 100kHz. By comparison, the Dynaco iron's overshoot was at about 60kHz. On the bass end, the 20Hz distortion from the James amp was about half that of the Dyna.
 
#293
SY said:
That's not too far off from what I paid, if anything it might be a bit cheaper. Last night, I was playing with the compensation in one of the James-based amps here and was very pleased to see that I had to suppress a bit of overshoot on square waves at 100kHz. By comparison, the Dynaco iron's overshoot was at about 60kHz. On the bass end, the 20Hz distortion from the James amp was about half that of the Dyna.
Click to expand...

This might be a silly question, but how does a Hammond compare to the Dyna? After reading the article, I think this would be a doable first tube project, but I'm poor and would like to cut financial corners (and still sound good).
 
#294
I haven't used any of the Hammond OPTs.

If I were to go on the cheap, the one I'd try is the Edcor unit:

http://www.edcorusa.com/products/transformers/xpp/xpp10-8-8k.html

If it didn't work, well, it's only $16. A nicer looking version is this one:

http://www.edcorusa.com/products/transformers/cxpp/cxpp25-ms-8k.html

Whether it actually performs better or not, I don't know, but I'll bet Edcor would give you a reasonable answer if you asked about it.

And finally, there's always the Dynaclone, which is pretty reasonably priced:

http://www.triodeelectronics.com/z517wadyoutr.html
 
#295
Well, it looks like I have my Tx troubles sorted. Heres 2 lots I won on Ebay last night:

ebay 1

and:

no. 2 ebay

I think I got them pretty reasonable, postage was $19 on each (ie 38 total). I think there were few bidders because the items are in Germany but the seller clearly aimed at the US market where the shipping was quite high.

I need to use one from each auction to give me the voltages, that still leaves 2 more over with a good range of voltages for future projects!

Now on to chokes, I think I'll use the italian co. for that, their shipping was pretty reasonable too. They also do resistors caps etc etc etc so I might try and get a lot of the stuff off them.

heres a happy camper (although wrecked, that bloody auction didn't end til 2.10 am and I stayed up for it!) 😉



Fran
 
#296
Just got the output transformers from triode electronics. They certainly do weigh quite a bit! Arrived very well packed and fair play to them, they passed under the radar!

Have to say it was a pleasure dealing with them, refreshing to get someone who doesn't charge a fortune to shipping (shipping cost was automatically calculated by the online shop, but was exactly the cost of shipping on the stamp on the box!)

I'd heartily recommend them to Europeans looking for Txs.

Fran
 
#298
SY,

I'm assembling a BOM for the RLD at the moment, prob in an excel sheet. Would it be OK to email it to you to double check me? - it'll be a couple of days yet before its complete.

If it works out ok, I could look into hosting it somewhere and posting the download details.

Another maybe stupid Q: you know the phase splitter/input 12AT7 - when you're actually building the amp, do you use one 12AT7 to do both functions per channel, or do you use one 12AT7 as a phase splitter for both channels and one 12AT7 as an input tube for both channels? Layout would lead me to believe the former...??

Fran
 
#299
The former. And that's OK as long as the heaters are biased up as shown on the schematic. I don't like mixing channels in a tube when I can avoid it, but I don't think it would hurt anything there. I have a higher resolution photo of the layout if the ones I posted aren't clear enough.

A small change since the original: the 1000uF cap on the heater string is much bigger than needed (I just happened to have one out when I needed it). 10uF is easily big enough. Also, the 45k3 are 47k (easier value to get, works fine), and the 135k plate resistor can be two 270k in parallel.

I'd be delighted to check over the BOM and host it (with appropriate attribution).
 
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