HST-11a (aka Apex 460) Mod starting

[Blue Jinn]

OK,

Another midnight mod project.

I picked up a pair of HST-11a's. These are unbranded, but are the same on the inside as (at least in the USA) the Apex 460.

I got pair of BV11 (5:1) transformers from AAmicrophones.

Mod will be:
Change tube to a 12AY7 (still need to order those from TubeDepot)
Swap out transformer and coupling cap (2.2uF)
swap in an edge terminated C12 inspired capsule,
eliminate some bypass capacitors.

Also, lower the B+ to 120v by swapping zeners in the PSU.

Credit for the mod goes to Dave Thomas.

The cathode follower (or apparently more precisely known as a constant current draw amplifier) will be maintained. This mod is slightly different than other mods I've seen which change to a plate follower circuit. (Also, there is a mod floating around which swaps out the stock 4:1? trafo for a 10:1 trafo, which to me doesn't make a lot of sense....)

 

[Justsomeguy]

Looking forward to this man. i've had my eye on the HST-11a and was just thinking about simply swapping the tube, but i'm very intrigued to hear how it sounds after your mods.

 

[Blue Jinn]

Swapping the tube is probably not a bad idea regardless, and the foxuadio guy's website says the stock transformer isn't too bad. They usually come with a 12AX7, which has way too much gain. Putting in a 12AY7 should help tame things a bit. I think unmodified the mic is too hot. But see this http://www.foxaudioresearch.ca/The460secret.htm regarding also getting rid of the capacitors on the transformer. So if you're not keen on soldering in new parts, you can swap the tube and physically cut out two capacitors, and you're out what US$15.00 for a tube?

 

[Justsomeguy]

But see this The 460 Mini-Mod regarding also getting rid of the capacitors on the transformer. So if you're not keen on soldering in new parts, you can swap the tube and physically cut out two capacitors, and you're out what US$15.00 for a tube?

Strangely enough i ended up on that website earlier this evening but purely because i was looking at how easy/how much effect ripping out some mesh in a different LDC would make. And that was completely my thinking; for £160 for the mic, £15 for a new tube and some snipping it seems almost rude not too I was bit concerned that Michael Joly had stopped modding them because he said the quality control on them had slipped alot of late (unless i misread that in another thread....) but i'm not expecting miracles, more just something to start to get my modding hands dirty (heck, we've all got to start somewhere). I bought a HRM-8b (Apex 205) with the intention of modding it but i kinda like it how it is

 

[Blue Jinn]

Ordered the tubes today. Should be about a week to get. Using EH, also got a NOS JAN 12AT7 for an MXL 9000. Another mod, in the drawing board stage. (That's a mod of necessity as I don't have a PSU for it.)