C28 Restoration

I am trying to restore a pair of C28's. I got them years ago as a "maybe you can use them for parts" present/kickback and have been steadily getting bits as they were needed and I can afford them. The last stuff I got was a pair of cap covers, a pair of plugs for the mics and 10 metres of cable from AKG. I was assured that the mics will not be affected by the fact that the cable is 8 core, but I am thinking that that would have a bearing. I would like to get the best cable. My next purchase is to be trannies and I would really like some advice on those. I am planning on building the G7 so perhaps Lundahl would be a good choice. The other thing is...I want to date them. I don't know wether they are A's or B's. Finally, would I be losing the run of myself if I went for valve rectification? Dual rectification? Cap suggestions for the PSU's switches, whatever. I would be grateful for any input. The brainiage exists surely?

I have not seen a c28 but from a fast look on the web it seems there are a few versions First what tube in yours a 6072a or nuvistor or ? I have not found a schematic, I will still look

Do you have a schematic? what type of gain stage CF etc? that would help with understand what type of transformer. Have you checked or emailed the Tab-funkenwerk site to see if they make a transformer for that model.

models

C28

C12

hey man, Id reccomend trying out one of the lollipop capsules from BLUE, it will mount on a c28, I use it on mine almost exclusively. If you make any headway with the transformer, please post info, I have an original one, Ive always thought the transformer was kinda not very good in this mic. Id love to put a new transformer in there.

If you need to see what one looks like all put together right, I can email you pics of mine if you want, its in really great shape. I dont have the original power supply (not that Id want it anyway) so I cant help you there.

dave

Thanks for the reply lads. I wish that I had more time to spend on visiting the forum. I have seen the Blue Lollipop cap thing but it's pretty dear for me at the mo.The money has to go toward trannies and other parts. Do you think it would be possible to make ones own "Lollipops"?

Ta for the links Gus. They're either A or B (6072). The mics had no bottles so I sprang for NOS 6072's back in '96. I have been told that the C (nuvistor model) aren't all that. I have schems (thanks to Karl at AKG) and all that but I really need to get some info regarding the questions I asked (cable issue, rectification etc). I will, without question, post my findings Soundguy. I just want to DIY it and make them beautiful. It is one of my life's ambitions to record my album with those mics and has been for years. (BTW, I cannot avoid having to disappear for days at a time so please excuse my mild inconsistencies .)

Dave have you had a chance to check the ratio of the transformer?

TriggerX what type of circuit is the microphone output off the plate or off the cathode of the tube to the transformer?

no gus, I havent gotten into this mic at all, I honestly dont even know if the transformer is in the mic or in the power supply. The mic body is big enough to house a small transformer though. The mic doesnt sound bad at all, its just got the very sort of tough angry sound that limited bandwidth transformers tend to have. Im sure some people love that kind of thing, if I could use a jensen in there I would in a second though.

dave

My flat got flooded on Saturday night and a lot of my technical data has been destroyed as well as a couple of amps, my clothes, a scanner, guitar synth etc. I sent an email to AKG requesting Karl Peschel's email address so I can get the schems again. I will be in touch.

The C28 has the exact same circuit and output transfomrer as a C12 but with none of the pattern control parts as the screw on elements are only 2 plate types in the C28.

451 screw on elements fit on the C28 as well.

I have the circuit if you get stuck.

Joe

www.jlmaudio.com

[email protected]

Hey Joe,
Thanks for the input. I got sorted with the diagrams from Karl and other data. I think though that I am going to have to gen up on my theory a bit. I was in touch with Tracy Korby and he does psu's for $375 each. I really want to build my own now though.