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Leak Delta 30 resto-mod thread

Markoneswift

Markoneswift

Quartz locked n ready to rock
Just opening up a thread to document this early Seventies Leak Delta 30 that I'm working on.

Initially, it was reported that one channel kept going out with a fuse blowing.

First steps were to replace all glass fuses and one broken holder. Brought it up on the DBT and it passed that test. Had to recondition the power lamp bulb holder, it was all corroded.

After running for a while, it was obvious that we had some issues because I was unable to set the quiescent current as per the SM and also some thermal runaway was occuring, heating up the whole amp AND the case to near unbearable temperatures - quite an achievement for an amp only rated at 15 WPC !!
 
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With this design, I was able to pull the pre and power amp boards out. We have one pre, one power per channel. The carbon tracks on the big old trimpots looked pretty bad and there were signs the BC143 drivers were running hot. R51 is a 1 watt 10 ohm resistor and that too was charred on the left channel power card.

I removed the trimpots and old BC driver pairs on both power amp cards. I could only find mini 200 ohm trimmers locally, so I installed those but extended the legs to fit the original holes. I also installed BD139 / 140 pairs to replace the old BC drivers. I also installed new 1 watt 10 ohm R51 resistors.
 
Whilst I had the cards out, I took the opportunity to check the filter caps - there are three 500uF / 63v and one massive 2500uF / 50v as standard. All of them, especially the big one, had crapped themselves so were removed. The big silver can 2500 piece was mounted upside-down in a clamp and when I took it out, there was lots of dry browm gravy all over the chassis floor ! The smaller caps had all bubbled up their plastic tops too.

To replace these, I had to go larger with the main cap from 2500 / 50 to 4700 / 50 as that is all I could find locally. The 500's were replaced with 470's as I figured that was close enough with tolerance etc. Going bigger might be better - I'm open to suggestions on that !!
 
I'm currently running a Sony Discman D250 (what an amazing sounding portable CDP !!) as my source and listening on headphones to Dire Straits - Brothers In Arms. The amp sounds great, even with cheapo Sennheiser HD201s :-) I'll try my Urbanite XLs shortly.
 
I'm replacing the output capacitors now. Both of the old 1000uf 48v caps read quite high (nearly 1500uf) so they are going to be changed to 1000uf 63v pieces.
 

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Markoneswift said:
I'm replacing the output capacitors now. Both of the old 1000uf 48v caps read quite high (nearly 1500uf) so they are going to be changed to 1000uf 63v pieces.
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Good choice. Output caps need to be the same capacitance as originals since they form a filter and changing the value will change the bass/treble emphasis.

That said, these caps in particular will affect the sound character. Your replacement caps look like fancier Nichicon "audio grade" caps. It that correct? Those should be fine and you can improve the sound a little by using Nichicon KL series instead (cheap) as they have 1/3 the leakage as all other caps (lower leackage = less distortion).
 
Markoneswift said:
I had to go larger with the main cap from 2500 / 50 to 4700 / 50 as that is all I could find locally. The 500's were replaced with 470's as I figured that was close enough with tolerance etc. Going bigger might be better - I'm open to suggestions on that !!
Click to expand...

Dropping down to 470 from 500 should not be a big problem, but you are losing a little capacity. Whatever that part of the unit that cap is supplying won't handle big surges (for power), so it would be fine for steady requirements like tone boards or the preamp board, but not so good if it were supplying the main amp board.

Bumping up power reservoir caps, especially going to the main amp board, is my favorite thing to do. That said, doubling the capacitance is ok so long as you prepare for a lot more inrush current, the big spike of current draw the power supply demands from the wall socket when you first turn the unit on. The larger cap will draw in considerably more current, for a brief time to fill up the cap, then it will level off. You just have to watch out for the components between that cap and the AC socket. I've found I feel better increasing the power reservoir cap when I'm also increasing the beefiness of the bridge, the fuses, any resistors and caps between that cap and the wall socket.

Not a dire warning; quite the opposite: "sounds good, just watch out for stresses in these particular components. and rock on!"
 
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Hi Mark -on these I find that the metal can transistors in the output amplifier cards are pretty reliable and sound great - so dont generally need touching.

But I see you have some of the ceramic flying saucer types in there - they can fail and get noisy - I always find replacing those is a plus.

Caps you shouldn't replace with "any old type" are the speaker output caps. The only time I have heard significant reversal of SQ is when I did this on a Delta 70 - I reversed my change and popped in some chunky Silmics to restore that fat, warm sound.
 
Thanks @slimecity for the info. I might switch back to the tin can trannies later - they checked out good on my tester so I kept them on one side just in case....

I am actually using 'any old type' output caps that I got from Jaycar for 3 bucks each. I'm inpatient and don't like waiting for onine orders to turn up. I don't like the minimum order for free shipping either !!
 
Yeah I hear you mate. I don't want to stockpile though because I do this stuff pretty infrequently. I just buy parts ad-hoc, as and when I need them. That does limit options to Jaycar though, pretty much.
 
Well, new 100 ohm resistors on the headphone output and two new 1000uf output caps solder in and.....wow ! This thing sounds phenomenal - it makes even my crappy HD202's sound wonderful.

Before these most recent updates, I could comfortably crank the volume to 12 oclock and still use headphones. Bass and mids were a bit muted. After the mods I now cannot go past 9 oclock and keep a comfortable headphone volume but there's no distortion, just full and tasty sound :-)

@slimecity I'm now hearing some noise / crackle in the right channel so I'm thinking that with the improved level of sound coming through, I'm hearing those flying saucers ! Any idea what you might have used to replace them ?
 
slimecity said:
Can you confirm what the numbers are printed on the actual trannies, what number they are in the SM and what board (pre or power) they are mounted on?)
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Power amp boards mate, BC154. They are T6 in the SM.

I'm seeing BC560 as a direct replacement but Jaycar doesn't carry that piece.
 
Yup - that sounds good mate.

But the BC560 comes in 3 gain types. You wont know to go with B or C type.

I recently replaced a few trannies in my brother's Stereo 30, I tested their gain on a cheap component tester to verify - then ordered the correct BC replacement type based on that. The SM is silent on the gain type.

I can also see a large & a small ceramic flying saucer trannie in your pictures - there must be another one there to replace?
 
slimecity said:
Yup - that sounds good mate.

But the BC560 comes in 3 gain types. You wont know to go with B or C type.

I recently replaced a few trannies in my brother's Stereo 30, I tested their gain on a cheap component tester to verify - then ordered the correct BC replacement type based on that. The SM is silent on the gain type.

I can also see a large & a small ceramic flying saucer trannie in your pictures - there must be another one there to replace?
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By large, are you meaning the black button -type one that further down the board ? The smaller ones that look like water towers are BC154 but I would need to check what those bigger ones are.
 
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