Winston O'Boogie said:Shameless name drop:
Attached is a pic of Beatles engineer Ken Scott and I with one of my RS.124 comps.
When talking to Ken about the RS.124 in use at Abbey Road, he mentioned there were a couple of times when he was using them in the cutting/transfer room when the needles never strayed from max compression (he said 20dB) all the way through the track.
Wish I could remember which particular Beatles tracks he was referring to but I'm not 100% sure now.
snod_donkey said:Might change the input transformer next too as 600 ohm primary might be a bit on the low side for some of the gear i want to run it with. I have a few Vortexion mixers which really want to see 10k or more to work best
Winston O'Boogie said:What you have'll work but, if it's a 600:10K in there, you don't need that much of a step up on the front end. A 10K primary with dual 10K secondaries is more in line with what was there originally.
snod_donkey said:I do have a valve tester here so will see if i can get a few valves that are a bit more matched up too
Rob Flinn said:What you need really is a valve curve tracer. The point is to get valves where their curves match so they are matched when the compression level changes. If you have them matched when there is no compression then there is a good chance they won't be matched when you have 10dB of compression happening & the bias is completely different on them. Something like a Utracer is a good test tool for this.
snod_donkey said:Nice idea. I will look into this. Have to say even when they are a bit off it is not obvious to the sound to my ears
Winston O'Boogie said:In the dozens of units I built in my time, I never noticed anything untoward either as long as both sides were decently balanced at idle.
At the time I started building these I coveted a Tektronix 570 curve tracer but, not having one, I did manually plot out a few valves at one point. Putting the best matched valve I'd found in a unit, I couldn't tell the difference in a blind test between that 'golden' valve and another that I'd done my, much easier, routine on:
Basically, I'd put a valve in, let it heat up and settle, then put the balance pot approx in the middle and measure the two anode voltages at rest.
Providing that was good, I'd run a tone into the unit at various levels and test the anode voltages at each point. If they were within a few volts of each other as the anode V climbed, we were good go.
Rob Flinn said:I actually agree with you. I have built dozens of vari mu compressors of all different types & repaired loads. I have an AVO Mk4 & a Utracer & have never needed to use either of them the get the units working well. Some compressors like a gates sa39 or 38 are a bit more fussy, but I have always got a match fairly easily by trial & error.
Juanaca said:Hello good afternoon, I am a fan of audio electronics, I need a couple of compressors vari mu my study but I do not have the comp economy to buy them or send them to build, so I only have the option to assemble them myself.
I have read the whole thread and I have not been able to find how many amps the transformer needs in its two secondary windings.
the voltage of one winding is 6.3v and the other is 117v, but I can't find any amperage.
that is one of my thousands of doubts.
snod_donkey said:Take a look at the valve data sheets that you want to use. This will give you the HT and heater current ratings you require
Juanaca said:Hi Rob, thanks for the pointers, this is not a thread for learners so excuse me.
However, to calculate the ohms law I think you have to know the resistance of each circuit, I have 120v but I don't know what resistance each winding has to calculate the intensity.
thank you very much
Juanaca said:So I think that in the 6.3v section with 2A it is enough, and with about 50ma in the 120v section it can work well.
I think I have the first step, now I need to decipher the rest of the scheme.
There won't be a thread to learn to read schemes of this type?
thank you very much
Juanaca said:Can you explain that better, Rob?
I have a toroidal transformer with secondary1 of 6.3v and secondary2 with 220v, how can I lower the voltage of this second to 120v without having to remove turns of wire and in the way that puts the least risk to my life?
Thank you very much