| 回覆 (29): 11A biasing voltage question |
| They are not cosmetically matched but 100% restored with matched components. I do not keep pictures in URL. I will send you the pictures showing the different chokes. |
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rsbn589
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12-12-16
21:04:01
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| 回覆 (28): 11A biasing voltage question |
KY,
Morning!
In the monaural era, monoblocs were produced as mono's and for mono. Two such mono's do not equal to a stereo. So it is important that *mono*blocs need to be matched when they were chosen and before they were paid for.
I guess they have been swop and became a matched pair if you still own them, right?
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rcwy
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12-12-15
08:07:06
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| 回覆 (27): 11A biasing voltage question |
Richard,
It is never late as long as there is a reply. it was confirmed by my friend that the different model of chokes (one is partridge and one is haddon) giving a delta of ~50V (if I still can remember it correctly). |
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rsbn589
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12-12-13
22:34:08
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| 回覆 (26): 11A biasing voltage question |
Hi KY (Rsby),
A lot late but if you are still having the worry, here is my slight input.
Based on your measurements in 2011, you were/are fortunate to have 2 matched pairs of EL34's, albeit not a matched quad of EL34's. Have you swop the 2 pairs between the two monoblocs? What were/are the measurements, then?
If the higher/lower measurement goes with the specific pair of EL34 when you swop the pairs, congratuation! it confirms the belief that your pair Audiomaster monoblocs is in good state. If the measurements sticks with the specific monoblocs irrespective of which pair of EL34 being inscerted, it may reflect otherwise on the monoblocs and/or on the 2 pairs of EL34's.
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rcwy
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12-12-02
05:18:30
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Cici
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11-11-06
19:15:44
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| 回覆 (25): 11A biasing voltage question |
Yes. You got me this time! 25V for both EL34 at one amp and 31V at the other amp. I do not mean to complain. I have real concern on any risk that would lead to damaging the transformer! I fully agree with you. The value is the amp itself. I feel like listening in fantasy Island when I first switched on the pair for just a few songs. Now I know why gingers is so fancy about this amp. My friend who helped me to restore the amps has no further warrant to the amps:-) The amps seems to run hot and we are scratching our heads by the 25V & 31V voltage measured. We are not so sure whether it is a norm or not. Hope to hear more comments from hi-hand here. By the way, thanks for your valuable inputs.
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rsbn589
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11-07-07
23:58:37
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| 回覆 (24): 11A biasing voltage question |
Ah, I think I made one mistake. So you saying one channel measured 25v for the cathode on both EL34s and 31v for both EL34s on the other channel.
If so, the answer is kind of similar as early described. Each amp works perfect but variations between L and R output valves not very well match.
Some valves were made to work hard and dont complain. EL34 is one of them! |
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bobui
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11-07-07
23:38:09
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| 回覆 (23): 11A biasing voltage question |
measured at 25V at one unit and 31V at another unit. Is it a remedy to just replace R16 & R17 with higher value in order to get lower (appropriate) biasing current for EL34 tube?
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Hey, no worry la! I am sure you would have heard from many other high hands here if what you have described earlier was at near danger to blow up and perhaps your friends would have already advice you.
The 25V and 31V difference indicated that the two EL34s were not very well matched. How about the other channel? The 11A is auto bias, right? so usually 10% variation between the output valves is kind of acceptable in the old days. And a few ma difference between two sides of the output transformer is kind of OK in the old days. Sure, excat valve matching is always the best!
Just in case you decided to plug in F2a11, kindly please pay attention to the balance or matching of the valves.
One last sharing from me. The valuable item here is not the EL34 or F2a11, its your irreplacable A11 that looking so cool and running! Agree?
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bobui
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11-07-07
23:18:17
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| 回覆 (22): 11A biasing voltage question |
| That worries me! The anode voltage is measured at 400V. Cathode voltage for both R16 & R17 is measured at 25V at one unit and 31V at another unit. Is it a remedy to just replace R16 & R17 with higher value in order to get lower (appropriate) biasing current for EL34 tube? By the way, I have not listened to modified 11A with F2a11 so have no comment about it. I have only listened to 11A with EL34 for a couple of hours. |
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rsbn589
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11-07-07
22:25:36
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| 回覆 (21): 11A biasing voltage question |
would be at 53mA-66mA
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I am interested to know how F2a11 sound compare directly with EL34. kindly share if you have that epxerience from your A11 amp.
And in return, I like to share with you on my understanding on EL34. 66ma on a single EL34 could be a bit on the high size if your amp is running above 400v because pa. 25W is the design max. 66ma at 400v is roughly 26W meaning your tube is being pushed hard according to Mullard spec. Some people say good old valves can be pushed hard and above their design spec. Choice is yours and really not so much on the valve but the limitation on your ouput transformer.
The most important is to bring equal ma between the two EL34 by adjusting the negative bias.
Oh, F2a11 has a 6.3v, 2A faliment as oppose to EL34, 1.5A. Just be extra careful not to harm the power transformer, please! The A11 is a good classic amp! |
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bobui
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11-07-06
18:51:33
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| 回覆 (20): 11A biasing voltage question |
Hi,
Is it a norm to get the measured voltage reading in the range of 25V to 31V at R16 & R17 on 11A? The corresponding biasing current would be at 53mA-66mA (25/470ohm-31/470ohm), which is extremely high for EL34?
Regards. |
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rsbn589
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11-07-06
14:07:43
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Cici
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11-03-12
06:10:54
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Cici
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11-03-12
06:10:04
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dkyyu
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09-03-01
17:19:04
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Tsushima1
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09-02-27
08:24:04
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mafat_576
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09-02-26
07:59:51
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mafat_576
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09-02-26
07:57:07
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Gingers
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09-02-14
10:05:18
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Gingers
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09-02-10
23:33:24
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Gingers
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09-02-10
22:04:40
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| 回覆 (27): Converting Audiomaster 11A / EL34 to Run F2a11 |
Morning Gingers ~
Yes I still have quite a few ( Too b****y many claims my wife ) and have tinkered with several others over the years .
As to favourites , Many Vintage amplifiers bring something to the party however Very few excel over the whole sonic range .
Symbiotic Speaker choice is also very important as you know , as can be the nature of the music itself ~
Of the Top of my head ~ a couple of Amplifiers that I would be sad to be without ~
The Audiomaster Is a Old Favourite as with XF1 together with a mix of Teflon and paper/oil capacitors it can rival many SE amplifiers in the Mid range , the Teflons extending the upper Octaves nicely as well as retaining the PP strengths in Base and drive , An excellent All Rounder .
For Chamber ensemble / Early classical and Acoustic the PYE PF91 excels as does the HF25 (especially when strapped in Triode mode) However So many owners do not seem to perform a thorough replacement of the passive components some of which can be hard to track down *especially the large electrolytics in the surface mounted cans * , when most if not all passive components are replaced and the feedback set up correctly they are Superb amplifiers.
Tim ~ Thanks to you I have made contact with Vincent .
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Tsushima1
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09-02-10
18:59:44
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F2aYeung
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09-02-08
12:38:56
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F2aYeung
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09-02-08
12:37:28
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Gingers
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09-02-08
10:42:47
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Tsushima1
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09-02-08
08:41:59
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timtube
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09-02-07
23:40:17
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timtube
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09-02-07
23:36:26
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F2aYeung
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09-02-06
22:29:40
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| 回覆 (21): Converting Audiomaster 11A / EL34 to Run F2a11 |
The output stage is very similar to Dieter's Williamson amp.
Check the center tap of the output cow primary and see if it's close to 430V. You can use 270 ohms for R16 and R17 if B+ is close enough.
Below is another F2a amp circuit for your reference |
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F2aYeung
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09-02-06
22:20:09
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ghost
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09-02-06
19:58:46
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Tsushima1
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09-02-06
12:31:26
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F2aYeung
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09-02-06
10:56:52
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| 回覆 (17): Converting Audiomaster 11A / EL34 to Run F2a11 |
Thank you for the further information gentlemen ,Your kind assistance is Much appreciated .
So aside from the valve base adaptor ( still trying to source these ) the only modification required to the standard circuit is to play around with the value of R12 and R13 ?
Gingers ~ I have just installed a V-Cap Teflon 0.047uf in a Test 5-20 amplifier prior to trying in the 11A ~ Early days however thus far = Amazing It is like removing a veil from the signal path . Hopefully the Teflon won't upset the tonal balance of the Audiomaster when I try this capacitor in the 11A .
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Tsushima1
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09-02-05
20:39:49
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F2aYeung
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09-02-05
10:59:18
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| 回覆 (16): Converting Audiomaster 11A / EL34 to Run F2a11 |
The optimal bias voltage for F2a11 is around 17 to 18V at around 400 to 420V B+.
EL34 amps will have a higher bias voltage with higher value cathode resistor (something like 350 to 470 ohms). You can try 250 to 350 ohms for F2a11 and see which value will get 18V across the resistor. |
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F2aYeung
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09-02-05
10:50:54
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| 回覆 (15): Converting Audiomaster 11A / EL34 to Run F2a11 |
Ginger
Thanks for posting the internal pictures of my Audiomaster 11a with F2a11 modification. I hope your friend can trace from the pictures how the modification to run F2a11 is done. I'll try to post more pictures later. |
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marantz7
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09-02-04
20:31:36
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Gingers
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09-02-04
19:59:23
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Gingers
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09-02-04
19:56:58
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Gingers
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09-02-04
19:55:10
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Gingers
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09-02-04
19:54:22
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