[S Clark]

I recently had Gary Dodd drastically modifiy a pair of Eico HF-12 6qb5 mono integrated amps.  He suggested that I change the Japanese 6ca4 rectifiers to improve the tightness of the bass.  I had a pair of somewhat weak Mullard's that I put in with great positive effect.  My question is, what is the typical audible effect of a rectifier getting weak?  Do they go all at once?  Can they cause other damage when they do go?  In otherwords, should these be replaced now?

Scott

[Listens2tubes]

Lower voltage supply, less volume and something sounds odd. Better than HUMMMMMM any day.

[iGrant]

On my amp it just stops making music if a rectifier goes (suddenly or gracefully). If it sounds great now as mentioned by Listen2tubes, wait for less volume and then replace.

Rectifier rolling is great fun, so you may end up exploring anyways

Cheers,
Ian

[S Clark]

If the lower voltage means less volume, then these are going to last a loooooong time since these little amps are surprisingly loud with a 91 dB efficiency speaker at just under a 9 oclock volume setting. 

As to tube rolling, there were large differences in the Japanese 6ca4, the Sylvania, and the Mullards-- with the Mullards the clear winner in clean bass. 

[avahifi]

If your rectifier tube is putting out lower voltage than optimum, then your tubes will not be turned on as hard as the designer intended.  This will lower their open loop gain, and assuming an amp with feedback, lower the feedback and increase harmonic distortion too.

In general, dynamics will suffer, bass will get muddier, and the entire musical presentation will loose clarity.

The advice to make sure you have good rectifier tubes is good advice.

Frank Van Alstine

[S Clark]

So a Mullard operating near new specs outperforms one that is still operational, but half way through its life.  Correct?

[ltr317]

So a Mullard operating near new specs outperforms one that is still operational, but half way through its life.  Correct?

I don't think so.  The Mullard, or any other tube halfway through its usable life will operate the same as a near new tube.  I think Frank is referring to a tube that's marginally good or worse. 

[S Clark]

Thanks guys. I think I've got a much better handle on rectifiers than before.

[Ericus Rex]

Happy to hear the issue has been rectified  .

[Niteshade]

Be careful of old tube rectifiers. Sometimes they tend to arc & short out if gas accumulates.

[BobM]

Can't you take Viagara for this. 

(oops, he said weak, not limp - nevermind)