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SE (UL ?) HI FI project needs help

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Hi to everyone and many thanks in advance for keeping such good Forum alive
I'm starting a new SE (UL ?) HI FI project. I managed to get my garage sorted and i found some interesting stuff

This were my findings

1 x PT from a Selmer T&B 100 (link)
http://www.drtube.com/schematics/selmer ... b100sv.gif

4 x GE KT88/EL34's/6l6 and many others

Lots of 12ax7/at7 etc, etc

A very nice aluminium plate about 400mm x 400mm x 3mm

2 mission freedom 5 spk's (link) http://www.dutchaudioclassics.nl/img/br ... 754-5f.pdf

...bits and bobs...

I'm a newbie when it comes to build valve amps unless I'm follow up instructions, schematics are fine I can read them, and I'm also familiar with components, high voltages, etc, but on the other hand, important details, like finding the right OT, or matching impedances, whatever else, can be a bit difficult for me, so I resorted to this forum for help.

My plan is
Build a SE UL (?) using the available KT88. I don't really need a power full amp, I guess around 15 W per channel or may be less, will suffice.
Using the parts already available to me if possible to keep the price low, but without compromising sound quality

I got a few questions if you don't mind to answer

Is the PT from the Selmer T&B 100 Guitar amp good for the project ? to use with 2 x KT88 mono blocks

The spk's are rated 6 Ohms and so far I wasn't able to find a match OT for the project (I'm in UK and there are many limitations sourcing PT's and OT's), I looked @ hammond website (link)

Hammond Mfg. - "Classic" Single Ended Tube Output Transformers - (1627 - 1642 Series)
but no avail.

Can someone recommend a proved and tested schematic for this project and a set of hammond OT's ?

Many thanks
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Only the Hammond link is valid. :(

Look at the model 1627SEA. Notice that the 6550 is suggested and, for all practical purposes, KT88s and 6550s can be interchanged. Perhaps full pentode (with regulated g2 B+), instead of UL, is advisable. That would allow anode B+ to be fairly "tall", which would mate well with the 1627SEA's step down ratio.

A single power trafo can't be used for 2X true monoblocks. You could build 3 chassis: 2 amp and 1 pseudo dual mono PSU. As high voltage umbilical cables come with several drawbacks, including safety, a stereoblock seems best to me.
I came up with this, for the Selmer schematic. If that's what you have the power trafo from, it should be hefty enough and 345-0-345 is OK.

Please don't copy that fugly bias supply. Buy a separate power trafo for that job.

Thanks Duttman, sorry that link didn't work for you.
I really like your idea, 2 or 3 chassis with power trafo sitting somewhere else, I can see a lots of benefits using contained components.
I will get to you on that, I need to learn more about power ground and audio ground, and how to make the connection between chassis.

About the BIAS, and as you mentioned the "FUGLY BIAS", will cathode bias work ok with this trafo or not, cause i was thinking in leaving that secondary wire alone, not connecting it.

There is no bias tap or separate bias winding shown in either of the Selmer schematics. Both versions half wave rectify the O/P of a dropping resistance connected to an end of the rectifier winding that feeds the B+ rectifying circuitry. YUCK! That very cheap method is seen in a number of musical instrument designs. IMO, that does not speak well for the firms marketing said designs.

Sowter is good UK source for magnetics, but they are not inexpensive.

I suggest you go with "fixed", rather than self, biased "finals". Don't throw B+ volts away. Also, a fair amount of heat will be generated by a cathode self bias resistor. The low weight (227.3 g.) and modest cost (7.05 UKP) of an AnTek AN-0130 suggest importing that item into the UK. Wiring the 2X 30 V. secondaries in series and bridge rectifying the composite with 4X Schottky diodes will yield you a highly satisfactory bias (C-) rail.
Hi, Grillo, I have had good results with the RH Universal amp which is an uncomplicated design and sounds excellent. It is a very proven circuit with many hundreds already built. With that design I made a stereo amp on one chassis that is not so big . The chassis was 7" x 17" with a Hammond 200ma x 800vct power trans and Edcor outputs. I also made a similar amp with a separate power supply chassis because I used a Triad 250ma power trans, 2 big chokes and 2 vintage oil caps and Transcendar OPT which were more manageable on 2 chasses.
The Hammond 25watt OPT is very big and will cost a lot to ship. Edcor makes a 15 watt unit that is less than 50.00 and is a nice looking and nice sounding unit. But, I don't know what it would cost to ship a pair to you. Good luck
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Only joking makes me feel a bit guilty, doesn't help you with your project :guilty: .
So how about something like this ? :idea:


  • KT88-12AX7-SE.jpg
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It's cathode feedback.Lowers the output impedance and distortion. But raises the needed signal level at the control grid (original voltage + speaker voltage)
So that will bring the output impedance level to around +\- 6 Ohms, correct?
can i still use 6L6/EL34 and other compatible tubes with that sch.
As previously mentioned by a member (link) RH Amplifiers: RH Universal v.2 – Totally Universal
this looks promising to me, I got a lot other tubes, just want to ask if the PT from the selmer will be a good fit.
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