Hiwatt SA 112 - Built On A Friday

[@HiwattOfficial]

Hey Brad, nice work getting this up and running. Sounds great at the end! Looks to be an approx 15 year old amp. For info, the chassis designs were revised when the new ownership came in in 2016. Wiring is back to the original twisted wiring implemented way back when as well! Hiwatt should be back in Aus soon too, so hopefully you'll get to see a new build in the near future!

[@BradsGuitarGarage]

Thanks for reaching out and clarifying! I look forward to seeing some more Hiwatt UK stuff in Australia as they certainly are beautifully built amps. Keep up the good work!

[@BenState]

thanks for showing interest.

[@thatampguy]

One of the few exchanges that gives me hope about the internet.

[@ReinoutVrijhoef]

Wow, this is a great reaction! Brad, keep up the good work, and thank you for all your videos and sharing your knowledge.

[@jtbracknell]

Brad, I appreciate your attention to detail on the amp repairs and sharing your knowledge with us. I know it takes time to make these videos while running a business and i just wanted to say thanks. I always enjoy the content, your sense of humor and always learn something from you mate. Cheers and much appreciated.

[@peeemm2032]

Enjoying the vids - especially appreciate the explanations, and the tips and tricks, particularly around safety. The touches of Aussie humour are the icing on the cake. Love your work 👍

[@weschilton]

Man, that thing sounds GOOD. I also noticed how much the hum was reduced after all of your work. Nice!

[@thatampguy]

Rarely see those in the shop. Appreciate the attention to detail!

[@smeh3929]

Дуже дякую за відео! Ніколи не міг би подумати що туретборт може проводити струм 🙂 Дякую, запам"ятаю цю особливість.

[@curtisc9350]

Damn, if Shipping wasn't so bloody expensive ! 🥺 You'd be the Amp Tech, everybody would want to send their Gear to . 😉 It's very intriguing to know, that a 4 Thousand dollar Amp built in the Uk 🇬🇧, is far from Perfect . 🙄 Thanks for your insight. The Hiwatt definitely sounded fantastic ! 🥰 After You provided the TLC , that it might not have had, coming out of the Factory in England ? 🤔 Keep up the great Content ! 👍 👍 Cheers ✌️ #bradsguitargarage #hiwattamp #hiwattofficial #customhiwatt50 #knowyouramp #knowyourguitar

[@xXsch3ricXx]

Great video. Thanks for being another tech around that goes the extra distance. Keep up the dodgy humor and content mate!

[@PsionicAudio]

More seriously, I see an issue with the stock circuit. If the HT fuse opens the raw bias might go well over the 63V that bias cap is rated at.

[@BradsGuitarGarage]

Ahh, yes. Good point mate. Still got the unit, so let's address that next!

[@goodun2974]

Similar bias circuit to that Dumble clone you worked on, Lyle?

[@ernestschultz5065]

Nice and roomy inside that chassis

[@Skman22]

Killer...I would love me that amp! Lovely work as always mate.

[@BradsGuitarGarage]

If you REALLY want it, drop me a line mate.

[@BradsGuitarGarage]

Stay posted for the JMP 2203 followup vid. I think you'll like that one, mate.

[@PsionicAudio]

But what about the Bugera Infinium?

[@BradsGuitarGarage]

Don't laugh, speaking of shit bias supply issues, got a BVV3000 here. Lol.

[@rabokel]

Beautiful wiring

[@rgbplumbinghilton]

great vid. At least Hiwatts are nice and easy to work on 🙂

[@wishbonebon7128]

Excellent video! Thanks!

[@erajad]

Found you through Lyle. :) Glad I did! I'm just a musician (wannabe) (not quite geriatric) with a lot of curiosity (and no expertise) in valve amps. Question on this "restoration": did you consider moving one of the output valves to one of the outer capped-off slots, given the overlap/promximity issue? or was that a non-starter for some reason? Thanks!

[@roncarter2188]

Bloody nice job, cheers.

[@retread1083]

Hey Brad, I don't know how those diodes in the SA-112 are connected but if they're like the diodes in the V4b where the cathode is connected to the OT and the anode connects to ground, they never see any condition where they conduct in forward bias. Their sole purpose is to protect the insulation of the primary winding of the OT (and the plates of the output tubes) from excessively high voltages that can occur when the secondary of the OT has no load. With no load on the secondary, when one tube is in cutoff and the other tube is conducting heavily, the (+) voltage on the plate of the first tube can reach ridiculously high levels. If the voltage between a leg of the OT primary and ground exceeds 2 x PIV (two diodes in series), the diodes fail and become conductive. This prevents the insulation from ever seeing extremely high voltage that could punch through and permanently damage the OT. When you exceed the PIV, the diode(s) will conduct hard and fast. The diode(s) will be permanently damaged, changing from crystalline to amorphous. The PS fuse will blow, and the diode(s) will need to be replaced. But that's a small price to pay for this kind of protection. Diodes and fuses are cheap. Iron is not. Fast recovery diodes shouldn't make any difference. Using them won't be better or worse. But a much higher PIV could allow for high enough voltages that the OT secondary can be damaged if run without a load. FWIW, 400 PIV does seem a bit low. They'll fail when the voltage from plate to ground exceeds 800v. I reckon 1N4005 or 1N4006 would be more appropriate. iirc, the diodes in my V4b are 1400 PIV (and they also use two in series on each leg).

[@BradsGuitarGarage]

Fast recovery diodes allow shunting of very brief spikes without continuing to allow current to flow for long enough to melt the diode. 3000-5000v PIV fast recovery diodes are used as a matter of course for flyback protection in many production amps from various manufacturers. The Blues Jr. for example uses the Rectron R3000F with a PIV of 3KV.

[@AROSFC]

those guys were made to fight distortion...🤣

[@vl292]

That looks like Hiwatt from distance, but didnt the Hiwatt stop existing early 80s or something. Or late 70s. But those original ones werent faultless either. I just had to replace power switch on my -75 dr103. How hard it would be to manufacture something that would last. No one wants to be changing parts every 50 years.

[@jbolt247]

Nice! You are the fuckery sorting master...

[@davidtaylor6124]

That thing sounds pretty good compared to a lot of amps on the youtubes, yet it doesn't seem to have all the things people talk about like twisted wires, heaters lifted away from other stuff etc. In fact it seems to have barely anything in it! What's the go with that? I envy your troubleshooting skills!

[@BradsGuitarGarage]

I've upgraded the audio gear so I'll do a sound test at full volume when I get a minute. It has straight heater wires which are very close to each other. It's not a very high gain preamp, so they get away with it.

[@valleywoodstudio7345]

You had that loud ! It took time for your mic compressor to recover to unity to hear your comments!

[@BradsGuitarGarage]

Yes, I'll try to find time to mic up cabs more often, but in the meantime, the slight clipping on the peaks gives an idea of just how bloody loud some of these amps really are!

[@valleywoodstudio7345]

@@BradsGuitarGarage I actually prefer the sound in the room more as you get some idea of Cab resonance and how it sounds to the player. Close mic always sounds less 3d than it does acoustically.

[@BadToad1963]

Wiggly wires FTW!

[@MrAletube]

those are the "Ken Fischer trainwreck " diodes,then perpetuated by Gerald Weber,if done properly with good quality diodes it shouldn't be a problem,as you stated,its better to use 3000V ones

[@BradsGuitarGarage]

Ahhh, so maybe someone has been in here before then.

[@fletches4084]

There's things about that amp that make me wonder if it isn't one of the fake HiWatts. I've a got a real one and it is all in the detail. That heat shield plate behind the power tubes looks very flimsy compared to the one I see in my amp (DR103). The Partridge stickers on the transformers don't look like they belong. The valve clamp positioning and so on. A good copy of a HiWatt can still sound fine given the design upon which it is based but for $4K I would expect to see a better job done.

[@BradsGuitarGarage]

Check out the earlier comment from Hiwatt themselves. They shed some light on this amp.

[@georgebush8038]

Bakelite is not a space age material .................for all you dinosaurs out there