What is this that has blown?

[budm]

Re: What is this that has blown?

http://uk.farnell.com/multicomp/mcrr...rad/dp/1216434

Are these ok to use?

Yes.

[mikay786]

Re: What is this that has blown?

Thanks, I feel bad just ordering those with free delivery. Must cost them 5 x as much just to deliver them

[stj]

Re: What is this that has blown?

http://uk.farnell.com/multicomp/mcrr...rad/dp/1216434

Are these ok to use?

the ones i linked are cheaper!

[fzabkar]

Re: What is this that has blown?

If you look at the board, there are two 470 Ohms 1W resistors, each one for feeding the Collectors of the Transistors, the Zeners are probably 12V, so they are not feeding the transistors directly with 39V.

Thanks. My eyesight isn't young anymore and I have bad colour vision.

Still, that is a horrible design.

A 1W, 470 ohm resistor would be able to handle 46mA at most.

The power dissipation in the transistor would be ...

P = Vce x Ic = ((Vin - Vout) - IR) x Ic

= [(39V - 11V) - (Ic x 470 ohms)] x Ic

So ...

I = 46mA -> P = 293mW
I = 40mA -> P = 368mW
I = 30mA -> P = 417mW
I = 20mA -> P = 372mW
I = 15mA -> P = 314mW
I = 10mA -> P = 233mW

AISI, that is pushing the limits of the spec for those transistors, unless the load is drawing some miniscule current. However, if the load current were indeed insignificant, then the designer could have chosen a higher resistance value.

Looking at it another way, let's assume that the designer chose a 1W resistor because it needs to dissipate 0.5W. Therefore the current draw would be ...

Ic = sqrt(0.5W / 470 ohms) = 33mA

At 33mA, the dissipation in the transistor would be 412mW.

[momaka]

Re: What is this that has blown?

they didnt know the colours actually meant anything!!!!!!!!

^
Yep, them colors are just for decoration and stuff. To make the circuit board look all pretty and colorful.

[mikay786]

Re: What is this that has blown?

On a more pleasant note ive finished with the technic units I scored a few weeks ago. Have come out great and really happy with them. Love the looks and the sound, powering some big old Jamo speakers which I though it might struggle with but has been fine.

Just took new AC cables and some of the pots needed cleaning out and working great.


Will be a keeper unless I find something better

[budm]

Re: What is this that has blown?

Thanks. My eyesight isn't young anymore and I have bad colour vision.

Still, that is a horrible design.

A 1W, 470 ohm resistor would be able to handle 46mA at most.

The power dissipation in the transistor would be ...

P = Vce x Ic = ((Vin - Vout) - IR) x Ic

= [(39V - 11V) - (Ic x 470 ohms)] x Ic

So ...

I = 46mA -> P = 293mW
I = 40mA -> P = 368mW
I = 30mA -> P = 417mW
I = 20mA -> P = 372mW
I = 15mA -> P = 314mW
I = 10mA -> P = 233mW

AISI, that is pushing the limits of the spec for those transistors, unless the load is drawing some miniscule current. However, if the load current were indeed insignificant, then the designer could have chosen a higher resistance value.

Looking at it another way, let's assume that the designer chose a 1W resistor because it needs to dissipate 0.5W. Therefore the current draw would be ...

Ic = sqrt(0.5W / 470 ohms) = 33mA

At 33mA, the dissipation in the transistor would be 412mW.

Easy way to find out is to measure the Vdrop on the resistor, and since current draws in the preamp section depends on the audio level it may not draw much at standby mode.
Typical Dual OP-AMP such as 4558 does not draw that much at all: They may have a couple of them for Low pass EQ.
https://cdn.badcaps-static.com/pdfs/...e2ada35a2a.pdf

[momaka]

Re: What is this that has blown?

On a more pleasant note ive finished with the technic units I scored a few weeks ago. Have come out great and really happy with them. Love the looks and the sound, powering some big old Jamo speakers which I though it might struggle with but has been fine.

Wow, they look beautiful indeed. Kind of hurts me when I see the dinged-up knob on the turner. I just can't imagine how anyone could mishandle/abuse old classic gear like this. To me, those old units are a piece of art.

I'm glad to hear you got them working and are using them . Feel free to post your setup in either of these threads:
https://www.badcaps.net/forum/showth...326#post586326
https://www.badcaps.net/forum/showth...047#post581047

[mikay786]

Re: What is this that has blown?

Wow, they look beautiful indeed. Kind of hurts me when I see the dinged-up knob on the turner. I just can't imagine how anyone could mishandle/abuse old classic gear like this. To me, those old units are a piece of art.

I'm glad to hear you got them working and are using them . Feel free to post your setup in either of these threads:
https://www.badcaps.net/forum/showth...326#post586326
https://www.badcaps.net/forum/showth...047#post581047

Indeed, and its more than likely given the clean condition of the amp it was probably the sellers (not original owner) who caused it.

Got my eyes on the matching cassette deck online which I will bid on and I'm thinking of buying the technics SB-F1 / SB-F2 or SB-F3 speakers. Perhaps going down the middle of the road with the F2s is the best compromise. Theres a MK2 version of the speakers, which probably sound better but not too keen on the looks. Think the MK1s fit more aesthetically, that's probably kind of silly as it should be about the sound!

[stj]

Re: What is this that has blown?

if you do a farnell order, why not replace the crap fuseholders you mentioned?

[mikay786]

Re: What is this that has blown?

I have, got them from maplins whilst I bought the wrong caps. Got two plastic type ones with covers on them.

[stj]

Re: What is this that has blown?

the cream coloured 20mm ones?
i love those - got myself a bag of about 20 from rapid a while back.
probably cost the same as your 2

[mikay786]

Re: What is this that has blown?

Browny cream, that's Maplins tax for you. I think they were 56p each so can't complain given the convenience.

[stj]

Re: What is this that has blown?

these 14pence ones!
http://www.rapidonline.com/Electrica...er-CFH02-64583

[mikay786]

Re: What is this that has blown?

Big thanks to everybody, this thing is freaking awesome. So much bass its literally sliding around on my floor!! Think I need to put it on some rubber or something.

So happy, my first proper sub. Thanks STJ, budm, momaka, fzabkar, ReeceyBurger123 and SteveNielsen.

[momaka]

Re: What is this that has blown?

So happy, my first proper sub. Thanks STJ, budm, momaka, fzabkar, ReeceyBurger123 and SteveNielsen.

Most certainly welcome!

So much bass its literally sliding around on my floor!! Think I need to put it on some rubber or something.

Nice!
Here, try this then:
https://www.youtube.com/watch?v=VzmbR-E6XYc

... and I'm thinking of buying the technics SB-F1 / SB-F2 or SB-F3 speakers. Perhaps going down the middle of the road with the F2s is the best compromise. Theres a MK2 version of the speakers, which probably sound better but not too keen on the looks. Think the MK1s fit more aesthetically, that's probably kind of silly as it should be about the sound!

Lol, yeah. You don't want to be embarrassed in front of people when you show that beautiful tuner/amp playing, only to make some tiny sound from those speakers.
I mean, don't get me wrong. Technics is a decent brand. But I would just avoid small speakers like that. They just can't match the performance of proper bigger speakers.