Audio and Video Talk > Valves / Vacuum Tubes

Manley Amplifiers

<< < (8/8)

So I decided to roll some tubes ...

Got some JAN 12AT7 USA (not bad), JJ ECC81's and Groove Tubes GT12AT7/6201 (one and then both seemed to have died... / quite shocking with the cost and reputation)
Having had some audible level difference as gain of GT12AT7 came into play I contacted Manley regarding the 5K/20K pot in the feedback loop between input tube 2nd triode. This compensates for the L/R balance when 12AT7/6414 triode sections are dissimilar. One can tune by ear of with signal generator/scope.

I also suspected one of my 6414's. I go some 5965's from Mrs Valve which Manley confirmed as a suitable substitute. 6829 will also work. 7062/E180CC might also as I read on some forums as the snappers also use the 7062.

6414, 5965 and 6829 are "computer" type tubes most I think have 10 000h heater life so a good choice as long time phase splitter. They were used under harsh on/off cut-off conditions in computer circuits. (when computers had tubes)

L/R balance is a whole lot closer to my ear  ;D

Tube         mu              Va(max)       Pa               Ia                Ra              S                 Rk
12AV7       41               300             2.7              18                4.8k           8.5                56
6414         43               200               2                 8                 7.6           5.5
5965         48               275             2.2                 8.25            7.2           6.5               220
6829         47               275             2.2                 8.5                7           6.7               220
7062         48               275               2                  8.5              7.2          6.4
E180CC      48              275               2                 8.5              7.2           6.4

Tube shootout 5965 types :

5965 operating points

I could only get a bias point with 5 of the 16 6p14-ER's I bought so I will mostly need to fiddle with master bias voltage...  ;D

Gee Gavin - trying your mighty best to ruin the lovely Eve-Anna's reputation?

 ;D ;D ;D ;D ;D

The figures given (also in the references) are textbook figures but do not tell all. It must be realised that especially Ra and S is quite anode current dependant. Thus in the amplifier the tube usually works at quite a lower anode current (Ia) than in these specs, often illustrative of r.f./switching conditions. E.g. for the E180CC, at Ia of 2mA, S is only 40% of the value at 8,5mA, and Ra is up by some 3.7 times. Also, these parameters vary quite sharply with signal amplitude round the 2mA mark. That is, they lie on an incline of S- and Ra-graphs which one tries to avoid during design (2nd harmonic distortion).

This not to depress, but just to show that rolling tubes which appear similar at a high Ia might not sound similar under conditions of lower Ia. So fine; that is why you try different types. But one also needs to make sure that the possibly different operating points are still in order for maximum signal. Tubes might sound better under your listening conditions but overload sooner. I believe this lies at the core of sometimes conflicting experiences with different tubes.

P.S: I also like computer tubes and use them for the reasons you state, but found that occasionally the two triodes in the same envelope can differ, computer requirements only being there for on-off states, not inbetween. Still.

Edit: Spelling   

It seems that 1 of the Halton 5965 is causing a bit of hum/oscilation so i am using the Amperex 5965. I have purchased some JAN GE 5965A's on Ebay and they also work well. Both Amperex and GE are clear top tubes with dual side getters so they look quite attractive!.

Have ordered some 6829's and 7062 from Ebay witch will ship soon.

5965 can also be sub for 12AT7/ECC81 and because of lower mu have less noise...

Substituted the ECC81/12AT7 on input with E180CC/7062. Quite surprising results.

Was lucky enough to buy a pair of IBM (Miniwat Dario) E180CC's (1960's) - see attachment.
Sounds very musical.


[0] Message Index

[*] Previous page

Go to full version