Dynaco st70 triode mod

[Audi0]

Currently I'm restoring a dynaco st70. With the Triode electronics mods.

I've hit a snag. I've waited a month for the parts due to triode taking there time putting it in the mail. They also gave me the wrong tubes I ordered but of same value. Plus more then what I ordered wtf

This is the snag the orange resistor is supposed to be good for 2w but it's really small. I think it's going to go explode when all is said and done. Is it 2 watts? opinions?

 

[Dave451]

I just refurbed the power supply in my Fisher 400, including new caps and resistors in the PS string. A couple of the 1W and 2W metal film units were quite small physically, but fully spec'd; about the size of 1/4 watt units from days of yore. I was a little surprised, but installed them and no smoke or indications of distress when I turned her on! They were maybe a little smaller than what you have in the photo. Good luck!

 

[Audi0]

I just refurbed the power supply in my Fisher 400, including new caps and resistors in the PS string. A couple of the 1W and 2W metal film units were quite small physically, but fully spec'd; about the size of 1/4 watt units from days of yore. I was a little surprised, but installed them and no smoke or indications of distress when I turned her on! They were maybe a little smaller than what you have in the photo. Good luck!

The one beside it is 2 watt resistor. That's why I was wondering.

 

[Dave451]

Agreed--it makes you wonder. The larger ones are more what I am used to seeing as "2W-size" resistors as well, but some of the new ones (like the Dane metal film units from Mouser) are quite a bit smaller. The larger units are how 2W MF resistors look from gear made in the 60's/70's. Maybe NOS units?

 

[airtime]

Could be a carbon two watter? the others are metal oxide. But I understand and agree with your anxiety. Better call and be safe than sorry.

 

[Dave451]

I'm pretty sure the larger one is definitely metal film. Just for grins, have a look at these (picture).
Left to right:
-Wire wound 5 W (compare to the old 'sand' 5W units)
-circa 1960s 3W metal film
-Current 3W metal film
-'Old School' carbon comp 1W
-'New School' Dale Metal Film 1W

How things change!
Dave

 

[Audi0]

I'm just going to assume it is the right value. If I did ask triode electronics chances are I would get no reply. Customer service is really lacking (I'm not the only person to say this). Also the caps that came with board are 20% tolerance. There so so on my meter the worst offenders are the 82 uf caps and read 70 uf.

Second question. I've read the ef86 manual back and forth several times. With no mention of this. The driver board screw holes are live. If we're to put the driver board in there it would either make the chassis live or is designed for some sort of ground?

 

[Audi0]

All the caps that are on the website look like nichicon(I could be wrong). The ones I got are Chinese nippon + 2 nichicons. Also look at the pic from the website(down below), the
orange resistors are rated for 1 watt but different resistance values. Looks like Im going to have to buy a resistor.
I got a few random resistors around.
Would 2 x 10ohm and 1 ohm cut it for now all are rated for 1 watt though.

 

[airtime]

I know this isn't the time to mention this, but consider just scrapping the deal and going over to tubes4hifi. Better boards and WAY better customer help. Bob puts together a great board and top notch parts. If it were my 70 I'd do it right.

Just been there if you're reading between these lines!!!!!!

 

[Lavane]

I'm just going to assume it is the right value. If I did ask triode electronics chances are I would get no reply. Customer service is really lacking (I'm not the only person to say this). Also the caps that came with board are 20% tolerance. There so so on my meter the worst offenders are the 82 uf caps and read 70 uf.

Second question. I've read the ef86 manual back and forth several times. With no mention of this. The driver board screw holes are live. If we're to put the driver board in there it would either make the chassis live or is designed for some sort of ground?

View attachment 819987

The mounting holes are on the board ground. So It will ground to chassis as it ahould.

 

[Audi0]

Well i will give a review of this mod when finished. I was told it "was good" and still is (sound wise) however from what i read owners have maybe changed at triode electronics. So maybe that explains why there cheaping out with parts.

 

[Audi0]

Got the amp running with the mods. Sounded quite good but ran into an issue. The speakers hum at idle or with no input. Soon as it has input feed it's like a quick pop noise and the hum disappears. Any ideas to what the issue is? Holding off on my review of the mods till it is sorted out.

 

[Audi0]

I worked out most of the kinks with it. Still has slight hum from the speakers. That may be normal. Ripped out most of the original black thin wires as it was inducing hum.

My questions are

1. The main transformer gets so hot after a hour of use, I would put it on part with the heat of the el34 tubes.

2. Should I even bother with removing the gz34 with the diode mod. The previous owner did it.

3. Review coming soon