Has anyone used Collins 356e?

Anyone used one or owned one? What are your impressions? I've got those GE's that are nearly identical. I'm looking at the schematics and have a couple questions.

Schematics:

Collins. http://img.photobucket.com/albums/v473/MikoKensington/Collins_356E-1.jpg

GE. http://photobucket.com/albums/v473/MikoKensington/GEuniSchem.jpg

What are J1 and J2 for? Metering? What might that pot by J1 be?

What is B+ and B-? I'm assuming B+ is 300VDC. Is B- ground? Forgive my ignorance, I'm trying to learn.

Also what's the best way to variac something like this. At the incoming mains?

Ýes, B- is ground. On J1/2 you can messure the bias voltage for the rectifier tube, but I don't know why one will messure this. With the pot you can trimm that bias, it's acts as a threshold pot.

If you have the manual it gives you voltages that equate to specific ratios and output levels, thus the J1-2 measurement points. That's why it's worth spending for the full documents.

Hey Miko, that GE looks alot like a 356e alright. I have a 356e and like it alot. I'd suggest an output pad of at least 20 db to keep from torching the inputs of whatever is downstream. On mine there's a 20db pad feeding a T attenuator. Without the pad the attenuator would probably be dead by now. I'm not sure what +56 db of amplication translates to in terms of wattage coming out of those 6v6's but i think you could drive a speaker with it no problem as-is on the schematic.

Also, an input T-pad adds a significant amount of control to the limiting and color.

Those measurement points are very useful for finding the sweetspots and for calibrating/setting the amount of gain reduction. I have a chart for the Collins which shows the entire range of voltages and corresponding gain reduction amounts, which is accurate when input levels are fixed, like +4db for example. The manual recommends a 23.5v threshold voltage for maximum S/N so I went ahead and made a mark on the faceplate (at the threshold pot) indicating this point, which usually is where I start when sending it a signal, then use the input pot to vary the amount of gain reduction and color.

Nevermind, I just needed to look at the manual for the pad values.

Thanks for the great info. I'm so glad this thread got revived before I built my clone. :thumb:

Highest output on the compression chart is 1 watt, though this is practically the same output stage found on the monitor amp from the same series, which does 8 watts max. You'll probably get close to this if you pull the sidechain rectifier and drive it hard enough.

I'm not sure what +56 db of amplication translates to

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Does this thing really do all this gain? Just wire the transformer primary for 150Z and drive it with a mic, like I do with my STA-level. Don´t forget to make a stand-alone Phantom power box, for using condenser mics with this. :thumb:

And if you stick an input control and an output attenuator, just like in the Gates Sta, you have a "kind" of threshold.

I'm not sure what +56 db of amplication translates to

Click to expand...

It translates to....56 db of gain. You have to have an input or output reference for it to mean anything other than 56 db more than what you had.

Collins manual says 54 db. Remember you're talking about 20-24 db just from the input transformer in most vintage pieces like this. Of course there's then usually about a 10-14db loss in the output transformer.

This one is really perfect for modding. Those 6V6 are exactly what you need to drive a faster sidechain. You can add attack and release controls and make it much more ecletic.

I think that this is the best way to use those old vari-mus. and you get one more channel of mic pre free. Sometimes I run my STA levels with no compression. just as a mic pre.

If you ever need to run a line throught it, just add a pad that would replect a higher impedance for the inputs, and say 20dB attenuation.

Use external phantom box, and you are done. This is really what I think is the best use for those. Drop me a line and I can send you more detais about the mods if you want.

http://www.groupdiy.com/index.php?topic=10134&postdays=0&postorder=asc&start=0

It´s not what I did in the end, but you can have some ideas by reading this thread. I´ll make a new drawing with the last moded version.

Raf - I'm certainly interested in mods for this. I have your StaLevel sidechain mod. Very cool.

Right now I'm just figuring out how to mount all of these massive transformers on the box. The 3A filament transformer is the same size as the output tranny. Both are freakin huge, and just barely fit in 2ru space on their sides. :green: