SimpleSE - motor run cap specs

[astrodog]

I know I have read somewhere about recommended specs for a motor-run cap for the Simple SE..... can anyone offer this advice, or point me to a link?

Its voltage rating must exceed line voltage and not B+ - correct???

[Ty_Bower]

Make sure it says "motor run" and not "motor start".
Something rated about 360VAC or higher should be good.
Look for something 80uF or more.

Maybe something like this one or this one on eBay.

[tubelab.com]

Its voltage rating must exceed line voltage and not B+ - correct???

The capacitor must be capable of handling the entire B+ voltage since it is directly conected to the B+. The confusion arises when we use AC rated capacitors on DC. There is a fudge factor that varies from 1.41 (conservative) to 2.5 or more depending on who you listen to. In any case a 370 volt AC cap will work in the Simple SE. I have used some 370 VAC motor run caps that I got from Ebay on voltages over 500 volts without issue.

I have not tried these two, but they should work fine.

[astrodog]

Excellent....thanks - will have a look around now - today I completed step one of the Simple SE build - built a workbench to build it on! (I have been banished from the dining room table after the last amp build!).....
Thanks
Lee

[astrodog]

Another SimpleSE question - I'm going to go with some Hammond 125's for OPTs - is there any benefit to getting transformers rated much higher then what the amp is likely to produce?? - the 125CSE is rated to 8W which seems plenty - will a heavier, higher rated transformer do anything for me - like the 125ESE?? I undoubtedly will never push the higher powers anyway.....

[tubelab.com]

is there any benefit to getting transformers rated much higher then what the amp is likely to produce??

In 95% of the cases the answer is a big yes. Why? Because there is no real standard for specifying the power handling capabilities of an output transformer. The power handling capability of an output transformer is not constant over the audio frequency range. The lower frequencies require more metal in the core and more windings to provide enough inductance. This means a bigger physical size, more iron and copper, and therefore more money. The unfortunate truth of the OPT puzzle is that size really does matter, and the cost / performance curve is pretty constant with a very few outliers. If I had only one ruler to measure OPT performance it would be weight.

Many output transformers (especially the Chinese ones found on Ebay) are specified at 1000 Hz. This is pretty useless for approximating performance with music. So, that "50 watt SE OPT" from Eastern Audio that weighs 5 pounds is like most other 5 pound transformers, a true 8 to 10 watt OPT.

Hammond actually specifies this in the text on the 125 series web page. Note the following:

Designed for general purpose or replacement use (not Hi-Fi), in single ended, tube output circuits.
Frequency response: 100 Hz. - 15 Khz at full rated power (+/- 1db max. - ref. 1 Khz).
For full frequency response (20 Hz. to 20 Khz.) - see our 1627-1642 series.

What does this mean?

Note the words "not HiFi", this does not mean that the 125's will suck when used in HiFi applications. It means that they will not work at their rated power levels.

Note the words "Frequency response: 100 Hz. - 15 Khz at full rated power (+/- 1db max. - ref. 1 Khz), This means that you can get 8 watts through a 125 CSE at 100 Hz, losing 1db of signal compared to 1KHz at an unspecified amount of distortion. I measure about 10%. At 20 Hz you can't get 8 watts through a 125CSE, it saturates at 2 watts, yielding 44% distortion.

The words "For full frequency response (20 Hz. to 20 Khz.) - see our 1627-1642 series." tell you that an OPT that will really handle 30 watts over the entire audio range weighs in at 11 pounds, and is priced accordingly.

Now, I have tested the Hammond 125CSE pretty thoroughly. It will handle under 1 watt at 20 Hz without undue distortion. This doesn't look too good, but how often do you listen to 20Hz? The lowest note on a bass guitar is in the 40Hz range where you can get 2 or 3 watts.

There are two situations where a 1 pound OPT works good. The first is a powered subwoofer situation where the main amp doesn't see much use below 80Hz, and the other is where the speakers have no real response below 80Hz. My Yamaha studio monitor speakers are dead below 70Hz so the 125CSE sounds reasonable on these speakers. I can still hear saturation effects on bass heavy music if the volume is turned up, but it is not terrible. You can't play techno on 15 inch woofers with these, it sounds gross even when turned down.

I have not tried the 125ESE but other users report good results. They might be a better choice if the budget allows it.

[korneluk]

Originally posted by astrodog
Another SimpleSE question - I'm going to go with some Hammond 125's for OPTs - is there any benefit to getting transformers rated much higher then what the amp is likely to produce?? - the 125CSE is rated to 8W which seems plenty - will a heavier, higher rated transformer do anything for me - like the 125ESE?? I undoubtedly will never push the higher powers anyway.....

Here are the 125ESE test results as reported by Joseph Esmilla:
http://members.myactv.net/~je2a3/OPTtestbench-1.htm

JE Labs 125ESE page:
http://members.myactv.net/~je2a3/125ESE.htm


Enjoy,

[chrish]

Originally posted by astrodog
Another SimpleSE question - I'm going to go with some Hammond 125's for OPTs - is there any benefit to getting transformers rated much higher then what the amp is likely to produce?? - the 125CSE is rated to 8W which seems plenty - will a heavier, higher rated transformer do anything for me - like the 125ESE?? I undoubtedly will never push the higher powers anyway.....

You may not have to limit your choice to Hammond. There was a thread recently about sourcing transformers in Australia, worth a look. If you are after budget or moderately priced transformers, shipping is high, but you can fit two output transformers in a US Postal Service flat rate box. Costs around $40 US to send anywhere in the world. I have had good experience with Edcor, they are happy to ship this way. I have suggested this method of postage to some Ebay sellers too and they have been happy to use it.

Good luck with the project,

Chris

[astrodog]

I did get a quote from Edcor - US$90 shipping..... I highly doubt this will be the last tube amp I build, so I'm sure I'll be getting other transformers very soon! Will give these a go and go from there.

I buiilt an S-5 K-8LS recently, and quite like the sound from its piddly little OPTs, so the 125's can't be too bad!

Maybe some of us Aussies need to group together for a big Edcor shipment!

[w5jag]

Originally posted by astrodog
Another SimpleSE question - I'm going to go with some Hammond 125's for OPTs - is there any benefit to getting transformers rated much higher then what the amp is likely to produce?? - the 125CSE is rated to 8W which seems plenty - will a heavier, higher rated transformer do anything for me - like the 125ESE?? I undoubtedly will never push the higher powers anyway.....

What George said, and a few comments from having 125ESE on a Simple SE:

The 60 ma current rating of the 125CSE will be easy to bump up against, and the 80 ma rating of the 125ESE is approached pretty easily with larger tubes, especially with slightly lower B+ voltages.

I would definitely get the ESE version, unless you are building a low power version of the Simple SE.

On the plus side, I think the 125ESE sounds pretty good on the Simple SE. It audibly benefits from cathode feedback, and cathode feedback is easy to implement with this transformer - just use one of the extra secondary leads. I am using the orange tap on mine.

I think the 125ESE were a better bargain in the past when they were priced a bit lower. The small Transcendars are about the same price, and they do sound very good on the Simple SE (better than the 125ESE and are good for 100 ma) and without any need for feedback, but lack the multiple plate load/secondary taps of the 125ESE, which makes the 125xSE series nice for experimenting.

I have some of the low cost Edcors, but haven't built anything with them yet. Everyone that has used them really seems to like them, and they may be the best budget choice.