CHRISTMAS SPECIAL (PT 3) - Are The Transformers DEAD?

[@ali2ndmail]

Thanks. This is awesome and is keeping me entertained and distracted from being poorly.

[@curtisprice9806]

My main Marshall 1987x power transformer was in a flood (Hurricane Katrina 2005). I didn't let it dry all the way out and long story short...when I crank up the voltage on a variac, my test light bulb starts to light up at just 60 volts or so ( USA 120v tap)! It means I have a short in the transformer . I heard crackling and a puff of magic smoke from testing it back in 2005 (it had not dried out completely and now I tested it again this year and the light bulb confirmed that I indeed have ruined it!) I could test it again with a fuse in line with the primary, but the light bulb confirmed there is a short in it.

[@hakonmoen3438]

great suff! nice little xmas calendar going on. Its been so much fun discovering your channel. Learning lots more making me want to go back into some project amp right away!

[@henryhunter5026]

I enjoyed watching you test the transformers. It must have been a bit of a relief to discover that they’re probably still alive and kicking as the cost of replacing them would be quite high. I was pleased that you stressed that messing about with mains transformers can be lethal and great care should be taken, if in doubt leave it to a professional.

[@nigeltrueman5931]

Enjoyed the video, Merry Christmas! Just wondering whether you think it worth using a Megger to test for contacts inside the windings? Also I'm wondering how you are going to clean the chassis. would a mild sand blasting be destructive?

[@GazCal]

Great video and information as usual Chris. Very much appreciate the lesson on checking transformer windings. .. I also always enjoy a good excuse for a spreadsheet. Am I correct in assuming Your secondary voltages for the 260V Tap input would increase due to a 244V mains instead of 240V. So HV of 347V.. Heaters at 6.43V .. etc.. 😊

[@RiftAmps]

The secondaries would decrease when running 260v primary on 240v mains 👍

[@GazCal]

@ hi Chris , thanks for the reply. Yes I understand the secondaries would decrease when running 260v primary on 240v mains, but I was just thinking your last set of figures on the sheet for the for the 260V tap would be slightly higher due to your 244V mains.... not meaning to be pedantic 🤓 just wondering if I understood the whole exercise correctly.

[@RiftAmps]

@ ah I see…I had already taken the extra 4v input into account 👍

[@paulp2033]

Great video and very well explained 👏👏 Also thanks a lot for the info on the schematics website. I found a great one there for the Selmer Treble n Bass. Merry Christmas 👍👍

[@74cannelle]

Everything you explained made sense. Could you say a word about the ultra-linear taps ?

[@curtisprice9806]

Yes...I have an old Peerless transformer with ULTRALINEAR TAPS from a 6L6 radio my dad built. This PEERLESS output transformer sounds fantastic in my AB 165 BASSMAN amp from 1965.

[@colinmaynard2879]

Better two lumps of iron than two lumps of coal this time of year.

[@alanpecherer5705]

The other thing I was thinking about for this amp, (earlier in this saga I suggested possibly installing a very long Twin Reverb parts board with room for 10-12 add'l components) would be, especially if you don't want to punch any new tube-socket holes in the chassis, would be to mount a long VERY narrow chassis with room for maybe three tubes atop the chassis. Parallel to the doghouse. That way, any pots req'd for the new circuit could poke out below the current front panel and you would not have to drill any new holes in the front panel...which always looks hokey. VERY rare for the transformers to be bad, but it's easy enough to check and would be a party-killer if they were.

[@rok4200]

If you have the possibility, you could use a AC power supply and feed 24V instead of 240V from the wall to test the mains transformer.

[@tgvettes]

can you check if a transformer is basically good thru Impedance/resistance test of the windings? Or is your method the only reliable way?

[@carlosanvito]

If the windings were all of the same gauge wire, a resistance ratio test would work. But, that's not the case. The HV windings are made of a thinner gauge copper than the filament windings, so a resistance ratio test is not valid. Voltage ratio tests are best, but must be aware that the voltages can be lethal.

[@johnnymoondog5818]

Following this project with a lot of interest, particularly regarding how you might voice the amp for both guitar and bass if that’s in your plan? I like Triode and Ultralinear modes, as well as Pentode, so keen to learn something. Thanks!

[@MyNameWasTecho]

Fascinating as always and lovely to get some Christmas Day maths. With the output transformer’s primary impedance having a roughly 15% discrepancy at 8 ohms but being fine, what sort of discrepancy would start to cause concerns? Thanks as always for the great content.

[@IAmChrisR]

Hi Chris, great news on the transformers! Assuming the voltages/impedance are all the same, would different transformers sound different (perhaps a different harmonic profile) and why? Would it matter more on the output transformers versus the power transformers? Would a similarly spec'd Hammond vs Heyboer vs Mercury transformer really sound noticeably different in an amp and how much so?

[@curtisprice9806]

Yes output transformer's change the tone for better or worse... definitely

[@davidlovellbass4761]

Are the differences between one channel of the AB165 and the UL silver plate bassman just the PI values, UL transformer taps and a few cap value changes in the tone stack?

[@curtisprice9806]

Get the schematics and look. Two different animals 4sure!

[@Bias_Prineus]

Hi sir, when i connect mine to the limiter it light a 30 watt bulb, and it trips a 10 Amper breaker, is it shorted primary?

[@williammiller9584]

Shorted primary or shorted secondary. Either way, unusable.

[@giulioluzzardi7632]

Happy Boxing day. I may have missed it but is the owner of the Bass-man playing Bass guitar or 6 string Guitar through it evenually? Thanks.

[@RiftAmps]

Both, but mainly bass 👍

[@giulioluzzardi7632]

Cool, a "Versatile amp". Do you think 4ohms works better for Bass guitar and 8 for Guitar?

[@pssmedia7134]

I didn't know a signal generator could drive such a load like 4ohms without dropping. Never done it.

[@RiftAmps]

It’s not driving any load…the transformer is unloaded. It’s nothing more than a step up/down device at this point.

[@pssmedia7134]

Off course..duh..

[@martinreid1740]

Fascinating stuff, and I managed to follow it along the way you demonstrated it.

[@petegreenwood2793]

Yes, the secondary winding reactance will form a pot-down with the output impedance of the sig. gen, which will cause a voltage drop. Best to confirm the drive voltage by checking the actual voltage across the secondary to ensure an accurate measurement.

[@watkinscopicat]

very interesting