CCA LA 1D Vari Mu limiter..any info on this ?????

[dustbro]

Final pics.

What a beauty!!
Thanks so much for sharing!

 

[pH]

for V2 and V3, is this schematic saying that pins 4+5 are tied together and get one side of the tap, and the other side is going into pin 9 (heater center tap)?

CT to ground, pin 9 to the other side of the winding (green).

 

[dustbro]

thank you sir!
so one side of green goes to 4+5, the other side goes to 9

 

[PRR]

> current value for L1 in the power supply...

Assume 200V-240V raw B+
12BH7 20mA
12AT7 3mA
0C2 10mA {(225V-75V)/1.5K}
6AL5 draws no power current.
==== 33mA

Filtering is not critical. Supply caps are large, all stages are push-pull, the low-level 6386 stage is filtered and regulated.

I could really see aiming for 250V-270V raw B+, then using a 1.5K 5W resistor instead of the choke.

Alternatively, the standard "Fender Replacement" chokes should work.

 

[dustbro]

Thanks for the info.
I ended up going with the Sowter CB24 Pi Filter Choke 18 Henry 70 mA
Been powered up and running non-stop for the last year with excellent results.

 

[GabrieleP]

We do need a PP 6V6 output stage to get the higher levels necessary to reach high ratios for limiting.

Are you saying (well, that was two years ago!) that being the voltage rectified by the 6AL5 considerably higher because of the 6V6 output, the control voltage is biasing the 6386 in a much heavier way? Am I getting it right?

But then again, limiting is usually applied at a higher level of the signal... How does one operate such a device (or a Gates STA-Level or a Collins)? Do you need a different mind-set?

I also wonder if a "6V6 limiter" would be the best option as a mix bus limiter?

Thanks in advance!

Best,

 

[envelope]

Hello, reviving the thread....

One of these just showed up on eBay, seller asking about $5K

Can anyone address the purpose of J1 on the schematic (looks like a 'connector' symbol, on the DC control voltage)

schematic is linked on the first post of this thread

Thank You.

 

[emrr]

linking or external control.

 

[envelope]

linking or external control.

Thanks Doug. I guess it s a 'jack' on the back of the unit?

Theoretically then, if one had a AGC1D and wanted a similar Recovery control as in the LA1D, but did not want to drill a new hole & relocate the power Lamp.. One could build a 'housed switch' and use a (very) short shielded cable to connect to J1. A fellow could build a few different controls with different timings as 'options', it is a nice looking device.

 

[emrr]

you can see it in my picture.

external control means anything you want to do with it, including fixed control voltage on a fader for VCA type control.

 

[envelope]

Thanks again for clearing up what the J1 symbol is.

turns out I managed to download a fuzzy 'thumbnail' of the schematic, But now I have the full size one and can see symbol and value clearly.

I have one coming in for repair, and will also report anything new here when the time comes.

 

[Woot]

Hi All,

I had a couple of questions re the LA-1D so I thought I'd resurrect this thread to keep all of the info together, as this thread contains some great stuff.

I have a pair of original AGC-1D's here and I am in the process of constructing a 1RU breakout box to add the extra release times as per the LA-1D schematic.

I have found a 5 pin novel connector that is the correct diameter for the fuse holder, so I will move the fuse inside on a bracket and add the connector to an external box to avoid punching new holes in the front panel.

I saw above that Doug used a basic switch for the release times, so I presume the control voltage is nothing significant. I had a look at the spec sheet for the 6AL5 but if someone could advise the sort of max. voltage the switch will typically see, would  be great.

I'd also like to bring the ratio/threshold pot out via this 5 pin connector too.

Can anyone see any downside to this? Voltages OK here too?

Thanks for your help!

Matt

 

[emrr]

Current and voltage  is well within the capacity of all but the weakest dodgy connections.  Typical wire and connectors such as used on a 500 series rack will be sufficient, assuming proper wiring protocols are followed.  mA is relatively low.  Look up the OC2 tube.  That tells you max voltage with ratio/threshold set highest.  Any lower setting is lower voltage.  Related potential current is through that same controls resistance plus the pair of 270K resistors. 

 

[Woot]

Hi Doug,

Thanks for the quick reply and the info. Makes sense, thanks.

I'll probably use some off cuts of tube mic cable for the box. The connectors I want to use are well and truly within rating for voltage current etc, as is the switch.

Another (perhaps silly) question: does the capacitance/resistance of the cable itself matter here? presume the values are so low as to be negligible over 60cm or so?

Cheers,

Matt