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    SP 14 Build Frank111

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    Frank111

    Posts : 83
    Join date : 2015-02-23
    Location : Minneapolis/StPaul Area

    Re: SP 14 Build Frank111

    Post by Frank111 on Mon Apr 13, 2015 11:02 am

    That would leave lastly, the two high voltage windings off the big transformer. I think the document indicated that only one section was used. Any harm or benefit to parallel these two HV windings?

    This is strange to have a transformer with so many unused sections on it.

    Frank111

    MontanaWay

    Posts : 767
    Join date : 2014-02-06
    Age : 58
    Location : Cameron, Montana

    Re: SP 14 Build Frank111

    Post by MontanaWay on Mon Apr 13, 2015 11:51 am

    I am not home right now, so cannot look up the model toroid used in the SP14.
    It should show on the circuit diagram what the mains should be for the B+ supply, either say 180, 200, or something like that. Then use that appropriate wire from the secondary HV, in the end you should use two wires, the 0V/grnd wire and the relevant HV wire, the other left over just insulate and tuck away

    MontanaWay

    Posts : 767
    Join date : 2014-02-06
    Age : 58
    Location : Cameron, Montana

    Re: SP 14 Build Frank111

    Post by MontanaWay on Mon Apr 13, 2015 1:48 pm

    OK, so your larger toroid is a model AS-5T240, meaning it has, on the secondary HV, a 220 and 240VAC tap, plus 0V.
    Looking at the SP14 diagram, you need to wire up the 220V tap, so just clip and insulate the 240V tap and tuck it away.
    Since pretty much all of the Tubes4Hifi preamps use off the shelve toroids, you will always have 'spare' wires/tappings on transformers which are not used, this is quite normal.
    When you get a chance too, take some photo's of your SP14 and post them here for all to see your great SP14 build! Smile

    Frank111

    Posts : 83
    Join date : 2015-02-23
    Location : Minneapolis/StPaul Area

    Re: SP 14 Build Frank111

    Post by Frank111 on Mon Apr 13, 2015 3:09 pm

    Will verify the model number of the transformer tonight, and once that's done, then I can finalize all transformer wiring and get ready for the final PCB wire up. You're help with the selector and attenuator wiring was a huge help! Just wanted to make sure I thanked you for that! I think that other builders will benefit from these posts.  I am willing to bet that no two preamp kits are built the same way. (Unless they are built for resale in quantity). Lots of questions have gotten answered here!

    Frank111

    MontanaWay

    Posts : 767
    Join date : 2014-02-06
    Age : 58
    Location : Cameron, Montana

    Re: SP 14 Build Frank111

    Post by MontanaWay on Mon Apr 13, 2015 5:36 pm

    Frank111 wrote:Will verify the model number of the transformer tonight, and once that's done, then I can finalize all transformer wiring and get ready for the final PCB wire up. You're help with the selector and attenuator wiring was a huge help! Just wanted to make sure I thanked you for that! I think that other builders will benefit from these posts.  I am willing to bet that no two preamp kits are built the same way. (Unless they are built for resale in quantity). Lots of questions have gotten answered here!

    Frank111

    as always, you're welcome. All on this forum want to make sure that you enjoy building your tube audio gear and then enjoy listening to it! Nothing worse than coming up against a wall with no way around it!!
    I'm pretty sure that toroid model is what you got for the bigger unit, got it straight off the SP14 docs I have on hand.
    That 220VAC HV secondary requirement should also show on the power supply circuit diagram which should be part of your kit assembly manual
    Don't forget to post photo's, of the in and outside of your build!

    Frank111

    Posts : 83
    Join date : 2015-02-23
    Location : Minneapolis/StPaul Area

    Re: SP 14 Build Frank111

    Post by Frank111 on Tue Apr 14, 2015 8:05 am

    The transformer is different from what the SP14 doc says. The number part number is AS-1T275.
    Here is the break out of the windings as stated on the transformer label:

    Secondary:

    275 Volts  (White/Yellow)
    275 Volts  (White/Yellow)

    6.3 Volts  (Blue/Green)
    6.3 Volts  (Brown/Orange)

    Primary:

    115 Volts  (Red/Black)
    115 Volts  (Red/Black)

    The secondary voltage is higher than what the doc sheet says it should be; (240 volts), and
    the primaries are both 115. My line voltage is over 120, as most are today.

    Now I'm wondering if this was sent by mistake? I know that with vintage electronic gear, the transformers had primaries of 115 volts, and with today's higher line voltages, they run hot and produce higher than necessary secondary voltages. Before I go any further with wiring, do you think this is the wrong transformer?

    Frank111

    MontanaWay

    Posts : 767
    Join date : 2014-02-06
    Age : 58
    Location : Cameron, Montana

    Re: SP 14 Build Frank111

    Post by MontanaWay on Tue Apr 14, 2015 12:12 pm

    well, that is certainly a different model toroid to what is indicated in the SP14 docs I have.
    Right now, it is better for tubes4hifi to step into this discussion for further advise.
    The AS-1T275 is a 100VA toroid, the SP14 docs I have show the model AS-5T240, which is a 50VA toroid, smaller in size and as you have pointed out, different HV secondaries.
    As to the 115V primary, even with our 120V, thats quite OK. As far as I can tell all Antek toroids have 115V primary windings, I've been using Antek's for a while with no issues at all, so this is not a real concern.
    Its the primary HV that needs to be sorted.

    Frank111

    Posts : 83
    Join date : 2015-02-23
    Location : Minneapolis/StPaul Area

    Re: SP 14 Build Frank111

    Post by Frank111 on Tue Apr 14, 2015 12:52 pm

    I'll hold off for now until we get this verified. I'll keep a watch out for his reply!

    pigface

    Posts : 68
    Join date : 2011-04-10
    Location : pittsburgh

    Re: SP 14 Build Frank111

    Post by pigface on Tue Apr 14, 2015 8:56 pm

    Best contact Roy . Sometimes when his supplier  is  out of the "normal" voltage transformer he will supply another that will work and switch some resistors around to bring the voltage bact to where it should be .

    Frank111

    Posts : 83
    Join date : 2015-02-23
    Location : Minneapolis/StPaul Area

    Re: SP 14 Build Frank111

    Post by Frank111 on Wed Apr 15, 2015 8:03 am

    Just sent this transformer question to Roy. Better to verify it for sure rather than assume!

    Frank111

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: SP 14 Build Frank111

    Post by tubes4hifi on Wed Apr 15, 2015 1:45 pm

    I check my emails hourly, I check this forum maybe once or twice a week, so support is always faster via email,
    but here's the answer I sent via email this morning . . . .

    yes, sorry, I should have sent the info with the chassis (I usually do when I have to make a substitution)
    Note that the windings come out in a circular pattern, it is essential that you use the correct windings, even though some of them have the same colors.
    Use ONE pair of the white/yellow to go to the HV inputs on the PCB.
    Use ONE pair of the blue/green to go to the 6v input on the PCB (this is for the rectifier tube filaments)
    Don't use the other pairs, just cut them off and insulate them.
    Tie both RED wires together and run to one side of the AC input connector.
    Tie both BLACK wires together and run to one side of the fuse.
    The PURPLE wire is the shield and goes to AC ground (the lower center connection on the IEC AC input).

    You will wind up with around 40vdc more raw B+, and so we may want to change the R23 set resistor from 330K to around 360K
    to give 289 vdc B+, either that or add a SMALL heatsink to the TIP50. I can send you either or both parts no problem, just let me know

    If you have any questions on the other transformer let me know. You would have either a round AS-0509 toroid (2 sets of 9vac outputs)
    or a blue square transformer with 2 sets of 7vac outputs. Those are for the left and right filament regulators

    Frank111

    Posts : 83
    Join date : 2015-02-23
    Location : Minneapolis/StPaul Area

    Re: SP 14 Build Frank111

    Post by Frank111 on Mon Apr 20, 2015 9:02 am

    Update 4/20/15

    I received the new resistors and heat sinks and made the changes. The HV AC from the transformer secondary is 285 VAC. The HV measures at about 295 Volts DC at the B+ points on the PCB.  The voltage at the 6X5 is 345 Volts DC.  Unless I hear otherwise, I'll assume these voltages are within the design range, and are ok although a little higher than stated on the instruction sheet.

    I finally have it assembled. Lots of checking and rechecking and it all looks good.  I went through my supply of tubes and found some NOS 6SN7 GTB's.  I have two NOS Tung-Sol's from the early 1960's. The other two are RCA's with silver lettering. I'm guessing from the 1950's. I tested them on my TV/7 DU military tube tester, and the are all a close match. I found a used Sylvania 6X5 WGT rectifier that is a brown base tube. It has a good balance between sections, did well when I dropped the filament voltage for a 'life' test. So although it's a used tube, I have decided to go with it because it really looks like a well designed tube. I'm keeping the tubes I got with the kit as a backup set.

    Finally, I just had a little time left for a very quick test to check on operation.  I used a small Magnavox boom box with an audio input and a tube Radio Craftsman mono tuner. I hooked it all up and was able to verify that the pre-amp does function. The attenuators work very smoothly up and down their range. Master volume control is working. The selector works properly. I had to check left and right channels separately because of using a mono FM tuner. But as crude as this test was, it got me to see that it functions. Next will be a more serious test where I'll hook the pre-amp up to my M-125 amps and use a CD player as a source. Probably use my Klipsch Quartet speakers as well.

    Progress is being made!

    Frank111

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