DIY Audio General - stuff you're making, tips, advice sought, etc


#122

So having swapped in some cheapo RFT 81s, the result is the same. So…

Help.

I literally now have no idea why the level is down, so the next step probably needs to be the cavalry who own the sort of scopes that can measure milivolt signals at non zero DC conditions where a Hantek does not cut it.


#123

And the cheapo RFTs may have shown possibly what the issue is. The reason behind the value of R17 was to drop the voltage to the point where the regulators dropped c. 10-15V at idle given an ECC81 running at 170V supply/4ma. However, with an RFT one section wanted to run at 165V for 4ma and one wanted over 178V and the valves @chelseadave sent me were still not dropping anything significant over the regs at 200V supply given the required current.

One properly balance matched ECC81 should therefore be on the way from Watford Valves and a selection of 5W Kiwames from 2K up to 4.3K to try in R17 given the particular requirements of the individual valve that arrives. Hey ho…


#124

Get it Anodised. Lacquering is no good


#125

I don’t think you can anodise copper. I think it would need to be an aluminium/copper alloy.


#126

^ This


#127

Polish it up with some metal polish, then give it a couple of coats of a decent car wax to seal it.


#128

polished and lacquered it 2 months ago and it’s still nice and shiny.


#129

This is the stuff to use on bare copper

https://www.everbritecoatings.com/copper.htm

However, if it’s still ok, why do anything


#130

Latest stage: got the matched ECC81, got a couple of the Diyhifisupply CCS modules to sit in the place of the LT338s (fed by the full HT voltage as they really can cope with it), got a massive 0.25 to 0.5Hz oscillation.

C2 was swapped out for some cheapo MKP 0.1uF that went into the parts bin from the Maplins fire sale and everything now seems to be working at last.

I may still need to tweak the EQ to make sure it matches between a bit as while there isn’t obvious colouration there is a little hint of images moving a bit, but otherwise I am now a) very happy b) needing to set up some inversed RIAA’d test tones c) going to buy some Mundorf 0.1uFs.


#131

I’m trying to get SME 3012 ready for the Yorkshire bakeoff, it had BNC plugs on the cable, so instead of just swapping them I’ve rewired the original connector with Van Damme and fitted phono plugs.

I now only have one channel :open_mouth: I’ve checked continuity from cart tags to plugs and all seems well. I’ve swapped over carts, and headshell still with the same result. If I put the shell in upside-down , and brush the cart I get both channels.

Any ideas?


#132

Mark, have you checked leakage between all the leads? They should be open circuit in every case with nothing connected, A higher than open reading between any two leads would cause this.

Thinking about it, the arm came off a deck that now has a 3009 fitted in its place so it might have had a problem.

Of course, if you are not satisfied, a full refund will be given :blush:


#133

Willow would like a return :slight_smile:

I’ve had the meter across most possibilities, my wiring seems OK with red n white going to the centre pins, and earth seems to be where it should be.

Puzzled :thinking:


#134

Just in case I wasn’t clear. Take the cable off. Meter between one pin on the arm end and each of the pins in the other end. You should get one short circuit and 3 open circuits. Repeat for each end. If the internal cable of the arm has somehow melted to another internal cable you will get a high reading and you will get problems like this. Do the same with the cable.

You’re both welcome back any time - look forward to Yorkshire bakeoff.


#135

I must have crossed the wires, or the headshell is wrong, I’ve crossed some and have sound in both channels.

Better sort a saggy counterweight now :wink: