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saletel 12th September 2009 04:23 AM

tubelab simple SE Tube selection help
hey guys need some help picking tubes for my simple se build. i just got got notification from digikey that my transformers had shipped. and i still have yet to order tubes or make a decision on what tubes to use.

im currently running some Tannoy 15" Red drivers one of the smaller rectangular cabinets the GRF (one of those right place right time things they were free!)

currently have a bottlehead foreplay III pre-amp.

anyway so on to tube selection and the transformers i ordered (i should have decided before ordering right? oh well) this is what the man in brown is bringing me.

(2)Hammond 125ese 12K-25K Primary, 1.5-15 Secondary 80 ma
(1)Hammond 274bx TRANSFORMR 2 FILMNT 375VCT 198VA

what tubes should i run to get moderate power and good fidelity out of. thanks for the input guys, tubes dumb found me.

boywonder 12th September 2009 04:45 AM

It looks like Digikey has the Hammond 125ESE specs incorrect (12K-25K) compared to Hammond's site. The 125ESE appears to be a universal 2.5K 5K or 10K primary with a 4 to 32 ohm secondary rated at 15W/80 ma.

Check out the tables on Tubelab George's site here:

The load Z column is your OT primary impedance. Each table has different tubes, B+ voltages, and cathode R's giving different power out and % distortion.

I would use the 5K taps on your transformers and choose a tube and other parts accordingly. The 2.5K tap on your transformers will result in more power out and higher distortion; notice tubelab's minimum load Z is 3000.

As a sweeping generalization, el34'S have excellent mids/vocals, and KT88's have better bass. The 6V6 is a lower power tube than the EL34, KT88 and 6L6 but is also a nice sounding tube.

How sensitive are your speakers?

Ty_Bower 12th September 2009 01:47 PM

The 6V6 won't work in his amp, the B+ voltage will be too high for them. He would have to choke load the power supply to get it down into range. If I were going to use KT88, I'd rather have bigger output transformers than the Hammond 125ese.

The last tubes I put into my Simple SE were a pair of Svetlana EL34. I was really pleased with how good they sounded. My pair isn't a "matched" set, just some leftovers I pulled out of the junk box. A new pair will probably set you back $60 or so.

If you're trying to keep costs down, I'd suggest looking at the 6P3S-E that appears all over eBay. You ought to be able to get a pair of those for just about $20, including shipping from Russia. They're very nice tubes, and I was happy with them when I had them in my Simple SE.

edit: By the way, does anyone know how to get image thumbnails to work correctly with the new version of the BBS software?

Tubelab_com 12th September 2009 11:58 PM


The 6V6 won't work in his amp, the B+ voltage will be too high for them. He would have to choke load the power supply to get it down into range. If I were going to use KT88, I'd rather have bigger output transformers than the Hammond 125ese.
Agreed. The 6V6 is a nice sounding tube but it requires a different power transformer. I use an Allied 6K56VG with them and Edcor XSE15-8-5K OPT's. They sound real good but you only get about 2 watts in triode and 4 in UL.

KT88's (especially the Electro Harmonix brand) make some big bass but you need big OPT's to get it all into the speakers. They still may be the best choice for big sound. As said before the EL34's have the best "detail" and midrange. Another popular choice for the least money is the Chinese 6L6GC. I have found them for as cheap as $4 each on Ebay, and $6 to $8 from major tube sellers. They are a very hard tube to kill (we know how hard I have tried and I still have the original pair) and they sound pretty good too.

With any of these tube choices, wire the 125ESE's for a 5K ohm impedance.

saletel 7th December 2010 03:44 AM

So i ordered el34s.

now i finally got a chassis drilled and layed out properly

now my question is how to wire my hammond 125ese for my 16 ohm speakers at 5k impediance like tubelab suggests (also suggests cathode feedback)

the taps are as follows with the picture


Thanks i thought i had this figured out but been away from the project for too long to make any sense of it.

saletel 7th December 2010 05:33 AM

ok so after looking at this a bit brown and blue go to t2/3-pri and 2 and 1 on those get jumpered? t2/3-sec gets black and white. (because at 16 ohms it will give me 5k ohm impediance im looking for correct?)

then i use the output phase that produces the lowest volume? (as written below)

Cathode feedback is used in this diagram. The secondary of the OPT's are connected to ground on the PC board so a separate connection is not needed. Note the reverse connection of the output transformer secondaries. This is needed on many OPT's to get NEGATIVE feedback to the cathode of the output tube. If unsure of your particular OPT's try wiring the secondaries each way (swap the two secondary wires, leave the primary alone). Chose the connection that produces the lowest volume.

w5jag 8th December 2010 04:13 AM

Blue goes to B+; Brown goes to plate of the output tube.

Use the white secondary lead to reflect a 5K impedance to the primary with a 16 ohm speaker load; black is the common.

The Hammond 125xSE does not connect up the same way as conventional output transformers with regard to cathode feedback. To enable cathode feedback, just connect one of the unused secondary leads to the cathode feedback terminal on the circuit board that connects to the negative end of the cathode bypass capacitor. You can play around with the different secondary leads and see if you hear any difference. They respond very well to cathode feedback - you can really hear it flatten the frequency response, it's not at all subtle.

I like to keep my 125ESE at about 65 ma or below for best sound, but I've put a lot more than 80 ma through them without damage.

You can find some pictures of how the 125xSE's are wired by looking at the under chassis pictures of my amp in the 6146 thread.


w5jag 9th December 2010 04:20 PM


You are declining e-mail through the forum so I am responding to your questions here:

You wrote:

"Thanks for the post on have a few questions i think you could answer quick for me (and id appreciate it) ive only built bottlehead projects before so this is taking a bit to figure out. wired up as follows. t3/t2 primary (1,2,3) blue(primary), green(secondary), brown(primary)audio t2/t3 secondary (1,2) black(16 ohm),white (0 ohm) now i blew the diodes yesterday (turned it on with hot tubes) so i clipped u10 and u20 ( i forgot about the dioddes at d1 and d2 was still blowing fuses then remembered d1 and d2) . Using tube rectification i need u10 and u20 correct? no music without them? without them the tubes would get heater voltage and thats it correct? currently no fuses blowing, but no music either. have choke wired up as well no r1 in place thanks -Eric"

1) If you are using Hammond 125ESE transformers, they are not properly connected to the board.

Connect the primary of the 125ESE as follows:

Blue primary lead attaches to T3 Pri:3 and T2 Pri:3. (B+ rail)
Brown primary lead attaches to T3 Pri:1 and T2 Pri:1 (tube plate / anode)

The 125ESE lacks ultra linear taps, therefore, there is no connection from the 125ESE to T3 Pri:2 or T2 Pri:2.

T3 Pri:2 and T2 Pri:2 should be jumpered to T3 Pri:1 and T2 Pri:1 for triode operation, or T3 Pri:3 and T2 Pri:3 for pentode operation. It is much easier to get the amp running in triode configuration, and I would suggest you start by wiring the amp for triode operation.

The white secondary lead should attach to the positive terminal of your speaker. The black secondary lead should attach to the negative terminal.

Forget about cathode feedback until you have your amplifier running. For now, connect a jumper across T3 Sec:1 and 2, and T2 Sec:1 and 2.

The Hammond 125ESE connects unconventionally regarding cathode feedback; the method of connection that I use is described above.

2) U10 and U20 are essential in all configurations of the amp; whatever you have done here, reverse it.

3) D1 and D2 are not essential if you are using tube rectification.

Hope this helps, let us know if your amp powers up correctly. Posting problems here will get a better response from a lot of different builders and help you get your amp sorted out faster.


saletel 15th December 2010 08:27 PM

Got it running. setup in triode configuration. no cathode feedback, no extra cap. will run it in this way then play around some more. thank you so much for your help.

saletel 17th December 2010 03:05 AM

so to get cathode feedback i want to run an unused secondary tap to t2/t3sec(2)? and ground to the other? sorry this is hard for me to grasp.

here it is running. wired in the motor run cap (hidden below) the chassis is tiny. here are some pictures grid looks hot on one tube, the other tube has a little blue on the inside of the glass which ive read is not a big deal (i dropped one tube onto carpet forget which though) colors follow the tube not the channel

the chassis is the high end hammond one they sell now with an aluminum top plate. only speaker outs are on the wood everything else is up top.

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