Repair of a vintage Robertson Audio Forty Ten power amplifier. Noisy Channel.

[@markrhine5809]

Dear Mr. Pier, Great video, You nerver give up until you find the problem. I know I have said this before, but you have an excellent channel, You do find fine work. You are one of my favor people to watch and learn from.

[@6StringPassion.]

Interesting amplifier. I think the epoxy-covered modules are there to keep the magic blue smoke from escaping.

[@radio-ged4626]

Nice cool-headed logical approach to solving a noise problem. The same with the "fake" DC fault. Shame the customer changed their minds, nice amp. Would offer to buy it myself if shipping to the UK was more affordable. I remember these coming out at the time, it was advertised in leading audio hi-fi magazines as a thing of quality, similar to NAD as far as marketing went in the UK. I'm sure others will disagree but that's my memory of them.

[@davidknightaudio934]

And if I had to guess those circle things with the bias pot ontop is probably full of diodes a capacitor and some resistors or maybe a vbe multiplier in a module mounted to the heating to couple the heat into it for the bias circuits thermal tracking

[@poormanselectronicsbench2021]

How unlucky can you get? Working on an amp with a DC coupled input, which is kind of rare, and having a DC offset on your function generator. It gives us something to think about before working on amps, I usually just worry about how out of tolerance, or leaky with age that first coupling cap is while going through things.

[@scrappy7571]

Good find on those transistors, wonder why they effected the other channel ? Too bad about the dead beat customer, UGH!

[@Poppinwheeeeellllllieeeeez]

Satisfaction from the repair and a few bonez.

[@DAVIDGREGORYKERR]

What about using acetone to depot the modules as they are know to cause problems.

[@trepanier01]

How much are you charging for it

[@neilstern7108]

Very interesting, I wish you could have played it though.

[@andershammer9307]

I have one of these. I don't remember if it's working or not. They made the 4010 and the 6010.

[@worroSfOretsevraH]

Do you know why they are always using resistor cores for those chokes? I never really understood. Some say for convenience. But I cannot see how a company that makes components, can't manufacture a simple core from some material.

[@marka1986]

In TV sets anyway, the resistor was there to dampen any peaks or ringing in peaking coils. So those coils sometimes were just wound right on the resistor.

[@treybennett9295]

Nice fix man

[@lox_5017]

Another nice video Jordan!

[@williamwong5627]

If I remembered right, this was an amplifier from Singapore. The owner is Robert.

[@SudburyMan]

Oh very nice.

[@markrhine5809]

Dear Mr. Pier, I keep hearing about off-set, can you explain what this is?

[@JordanPier]

A dc amplifier operates at a positive and negative voltage,.with the speaker output between the two. Since music is AC the voltage will swing appropriate to produce the sounds being heard. An offset is when the output is no longer 0v DC. This is an error that must be corrected or DC energy will heat up the voice coil of the speaker and burn it up

[@deukanand1195]

Any chance we could get a video that explains how to set up light bulb "fuse" or load sponge I guess I'll call it. Any special equipment required? - electrical novice here.

[@richpayton7162]

Are you talking about a dim bulb tester, aka DBT, used to prevent damage to an amplifier being tested? It limits current through the amplifier by inserting a mains voltage rated incandescent lamp in series with the "hot" lead of the circuit powering the amp. Different values of current limiting can be employed, starting with a lower wattage bulb and increasing bulb wattage (increasing the bulb wattage = decreasing the bulb's resistance = allowing more current. Here is a simple DBT video showing how to build it: kzbin.info/www/bejne/iGOtlmSnjNZjnq8

[@deukanand1195]

@@richpayton7162 Thank you!

[@davidknightaudio934]

Jordan the boxes that say svr on them a reverb tanks I think

[@davidknightaudio934]

This amp apparently has reverb

[@steveoszman8746]

You are the man.

[@markpirateuk]

Yes, 60 watts per channel, you will hopefully sell it at twice the price of the repair, I have the same problem with customers, most of the time I sell on the abandoned equipment on ebay😆

[@JordanPier]

I did find it a home this morning and still made out ok.

[@tntreviews3602]

HAY Jordan I hope you are doing ok haven't chat in a wile.

[@JordanPier]

Doin as well as I can right now. Money is tight these days and work is thin!

[@tntreviews3602]

If u need more projects to work on let me no.@@JordanPier

[@justsumguy2u]

Deadbeat customers, gotta love it.....but at least you didn't have much money into it. And great job of troubleshooting, especially without a schematic

[@zx8401ztv]

I hope you charged the customer for messing you about. So so annoying :-(. what a shame. Each channel reminded me of the insides of a stk or similar amp modules. But using uprated outputs. I like the potted bias presets to slow the heat and damp getting in. Not sure about the potted optical doobries. It's a shame the company failed.

[@JordanPier]

Oh yes, everyone pays diagnostics up front, which covers the first hour. Then some earnest money before I went forward. That's why I was confused why he bailed on it. He already had the majority of cost into it.

[@zx8401ztv]

@@JordanPier Some people make no sense at all, silly owner lol. I should have known about the diag charges as i watch Ivan at pine hollow diagnostics, a really decent man. Much like you, he always does great diags and a really nice man :-D. No im not buttering you up, i mean what i say.

[@wcovey9405]

Not sure you worked the power problem right. Using OMNS law, ((E*E)/R) = P; Your meter voltage is 22 Vac RMS. Say your R is * 8 ohms. Your DC voltage should be 11 Vdc RMS. ((11vdc* 11vdc)/ 8 ohms) = 15.125 watts RMS. making you peak power around 30 watts.

[@rogerknapman1260]

Nah, he got that right. The reading was an 22V AC RMS reading. Measured rails at +/- 40V. Therefore without rail sag he could have had 40V peak ~28VRMS. Obviously without a huge transformer you would have sag and you can't really drive right to the rails. So 22VRMS (33V peak) seems totally right. Vdc RMS isn't really a thing BTW.

[@wcovey9405]

@@rogerknapman1260 Yes the amp should but out more then 60 watts maybe 70 watts. Like the P.S. lay out, in my eyes it is just the best. Across a 8-ohm load, with a 21-volts rms, works out to 56 watts rms. I would think that with +/- 40 rail Voltage, for an eight-ohm load, the load voltage would be between +/- 30 to 35 volts which will work out to be more then 60 watts.

[@ThejasonJaw5442]

Never heard of them

[@enginecrzy]

so THATS nice...

[@technixbul]

Oh well until it comes to eastern Europe it will cost as much as 3 like this one :D

[@jdmccorful]

Nice work! Enjoyed watching. Thanks!