500 series PTP

[johnheath]

Hi all...

I have some thoughts to create a 500 series tube micpre and I would like to try to build it ptp.

But I know that I will need a the contact strip (don't know the word for it really) and I wonder where I can buy those contacts and I also wonder if it would be possible?

Inputs are very much welcome.

Best regards

/John

 

[ruffrecords]

Your main hurdles will be power supplies, heat generation and space.

The permitted  per module current draw  from the power supplies for 500 series modules is quite limited.  I think it is something like 120mA per module. If you have a couple of 12A?7 tubes with their heaters in series then that's 150mA for starters. I suspect this is the reason why most commercial tube based 500 series modules are double width. Then you need to generate some HT. Usually a switched mode PSU is used for this. However, if you need just 10mA at 320V for example, this will draw 100mA from a +-16V supply even if the switcher is 100% efficient. I suspect this is why most commercial tube based 500 series modules have just one tube  for the 'sound' and the rest of the signal chain is semiconductor based.

Heat is less of a problem than you might expect. My EZTube Mixer modules are close to the size of a double 500 series module. They contain three tubes and even when fully enclosed the outside of the module only rised by about 20 degrees.

Tubes are not small and for balanced inputs and outputs you will need transformers. Mic input transformers are quite small  but output transformers are rather big. Squeezing two transformers and two tubes into a double width module will be a Challenge.

Cheers

Ian

 

[[silent:arts]]

You mean something like this?
http://capi-gear.com/catalog/product_info.php?cPath=87_88&products_id=401

I should have some left inside the EU.

 

[johnheath]

Ian… yes, my guess is that space will be the greatest challenge in this case. I have an idea of an nice preamp based on two tubes… input transformer but without an output transformer so some space savings there. Since we "chatted" the last time about the poor mans eq I have tested a circuit based on a EF86 as first stage and a 6922 as SRPP final stage.

I am pretty sure it will work but my main concern is the coupling between the pre and power supply… "How do they do it?" Perhaps a 5-pin XLR?

Silent:arts… Yes, that might be the solution. But do you know if that type of contact has limitations concerning higher voltage lit 300vdc?


Best regards

/John