Quad 34/405 Dilemma.

[Speak]

Hi,

Check balance potentiometer, I have repaired on two Quad 34. The metal slides is fixed in plastic holder and the plastic cracks. I fixed it by melting the metal slides back with the solder.

 

[Zulu95]

Hi,

Check balance potentiometer, I have repaired on two Quad 34. The metal slides is fixed in plastic holder and the plastic cracks. I fixed it by melting the metal slides back with the solder.

Thanks for the suggestion. It seems OK but I'll keep it in mind.

 

[Zulu95]

Measuring the value (capacitance) of electrolytics doesn't usually yield any meaningful information in much the same way that measuring the terminal voltage of a battery gives no clue to how good it may be at delivering any useful current.

Make notes and take pictures so that you know what goes where and what the polarity of the caps are.

You read my mind as that is what I intend to do just in case something gets crossed.
I was actually checking condition but it was not conclusive. I did a lot more interweb reading at the best sites, from all accounts, and decided it was worth some of my time to fix instead of wholesaling it out.

 

[Mooly]

Its definitely worth fixing, yes

 

[Zulu95]

Update:
I did a complete recap of electrolytic and tantalum caps. For the disputed polarity and tantalum I used Nichicon Muse ES Bipolars and the for the others Elna RFS series. I just powered her up and WONDERFUL!!! My little friend is back in all "her" glory. This really was a labor of love and now I am happy to pass the Quad on to a new owner who should enjoy the classic Quad sound.
Thank to all here for suggestions and encouragement and to those who posted the vast reservoir of articles and suggestions online for all to access.

 

[Mooly]

Thanks for the update great to hear its all worked out well.

 

[Zulu95]

Well the saga continues: The 405-2 started "acting up" and an investigation of the main PSU caps and the two amp board caps revealed that I could not put the soldering equipment away just yet. Another Digi-key order should be on the way to me shortly. Then, hopefully I'm done.

 

[Mooly]

All good fun. If the 405 uses any of the ROE brand of caps (small round cylindrical with a 'Bakelite-ish' case) then those should all be replaced with good quality commercial grade electrolytics.

 

[Welcome]

Oh man, ROE parts. The bane of all old european electronics! Good thing we've learned to use japanese capacitors by now. It only took far too long.

 

[Zulu95]

Yea those ROEs are to be rued. They are cracked and failing. I pulled one of the PSU caps and it is reading short so it is shot! Getting replacements to fit the holders was my main problem. Now all the main caps will be an inch shorter that the originals.

 

[Zulu95]

All recapped and sounding beautiful. Better than I remember new! Well as good as at least. I upped the PSU caps to 15,000 uF so they fitted in the original holders.
I really enjoyed the project and would do it again in a heartbeat but hopefully not on the one I just completed.

 

[Ian Finch]

Excellent, may it give you many more years of enjoyment It shows that capacitors do age, even in low power gear. However, I trust that the greatly increased power supply caps combined with probably lower ESR, won't lead to failures. I realise you had a size problem with the main PSU electrolytics but on start-up, greatly increased capacitance also greatly increases the surge current and that could stress power supply parts like the fuse, switch contacts, transformer etc. These will be light duty types to suit a low power device like a preamp but I couldn't say how susceptible those in the Quad 34 might be.

 

[Zulu95]

I searched for a while to get as close to original I could. I was aiming at making it look like OEM. To this end I even raised the cap/holders on 1/2" spacers to get them up out of the bowels of the amp.