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15th July 2009, 10:25 AM #1.
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Reproduction Retro 40`S Radiogram questions.
Im making a retro 40`s style stereogram and want to include a valve amp mainly for the “visuals” I want the valves to be visible, so looks are more important than pure sound quality.
Thanks Cliffie….
Your links are great, way out of my price range but the configuration of the vales is of real interest as I will go with great advice from Zaphod of using valves in a fake way with separate power, as I already have the choice of an older NAD or Cambridge Audio amp. Also will have a Rotel tuner, and looking at an old Duel TT that plays 78`s and I want to add blue tooth and internet radio. Below is the full scale drawing of the cabinet and will be made from Walnut, Macassar Ebony and Black bean. Will be a fun project and I might do a WIP
Thanks Zaph, some great advice there. Ill do a google on EVACTO and see what they have. Im assuming someone with basic electronics expertise can hook them up?
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15th July 2009, 10:43 AM #2Senior Member
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Very simple stuff. Once you've found the valves (stick to 12.6 Volt and 6.3 Volt types only) you need only find the appropriate pins to connect to your heater supply. 12.6 Volt types can be easily configured to work on 6.3 Volts. Valve data is easy to come by. I have a shelf full of data right behind me.
You could 'phone EVATCO and explain what you want to do. They may have some valves lying around that no one wants that they'll sell you cheap(er). Tell them it's for retro-styling only. They may have some good suggestions.Last edited by Zaphod; 15th July 2009 at 10:45 AM. Reason: Brain fart
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15th July 2009, 11:18 AM #3.
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Zaph, how much heat will the 12.6v Valves generate? They will be inset into the red area with the amp just above (blue) then Radio (Yellow) Will the top, bottom, sides and back of the valve inset need to have some insulation and vent holes at the top? It will have Macassar ebony veneer in it (with quality heat resistant lacquer)
Also would anyone have a good suggestion for the speakers? I want that big warm old fashioned sound . My Cambridge Audio p70x gives that, so would the Jordan 4" metal cone be suitable? I have heard them and love it, but is their a cheaper alternative
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15th July 2009, 11:49 AM #4Senior Member
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Small 12.6 Volt types (12AX7, 12AU7, et al) will disspate around 2 Watts. I realise that you probably need to know what the bulb temp is. I can't tell you with any precision, but my (VERY) wild guesstimate would be that the bulb temp would be around 60oC. I will locate a suitable valve, hook it up to 12 Volts and enclose it in about 1/2 Litre container and measure the temperature rise. I'll let you know after lunch.
If you thought the discussion about valves vs. transistors got weird, don't even THINK about discussing speakers. Here's my thoughts:
The Jordan drivers are very impressive units. They're also Hellishly expensive and a little inneficient. Personally, I prefer a small bass driver + tweeter, since the sound can be tailored somewhat, the efficiency higher and the cost can be considerably lower, for similar performance. I would not call the sound of Jordans "old fashioned". That's just my opinion though. Speakers are all about opinions.
I have a couple of these lying around:
http://translate.google.com.au/trans...%3Den%26sa%3DG
And:
http://translate.google.com.au/trans...%3Den%26sa%3DG
And:
http://translate.google.com.au/trans...%3Den%26sa%3DG
These products are high quality and provide excellent results. Alternatively, some of the local suppliers have kits which may suit your requirements.
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15th July 2009, 02:08 PM #5Senior Member
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I placed a 12AX7 into a small cardboard box (An Australia Post video cassette postal box) and connected a heater supply. I let it run for about an hour and measured the result.
Ambient temperature - 18.5oC
Bulb temperaure - 45oC approximately (It's tricky measuring the temperature of glass)
That should provide some ideas for what you can expect.
In my explorations, I uncovered a half dozen ECC91 valves. They look nice, since the cathode structure is exposed and it glows a nice, dull red. See if you can find some. They should be cheap, since they don't appear to have much use in audio.
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15th July 2009, 08:53 PM #6.
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Thanks for doing that. 18.5oC is reasonably hot in a small area, so ventalation would be a must. Good to know now
So what would be some "big and wild" looking valves. I looked at This mob
because the are close to me. These seemed ok for the price.
Chinese Valve Arts KT66 @ $48
Genelex Gold Lion KT66 @ $58
Electro-Harmonix 12AX7 @ $18
JJ E88CC GOLD @ $44
And you know the "cages" you see on the valves, are they available commercially or made specific for the Amp makers.
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15th July 2009, 11:37 PM #7.
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16th July 2009, 08:42 AM #8Senior Member
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18.5oC was the ambient temperature of my workshop. The bulb temperature is the one you need to be concerned about. With the 12AX7, that is around 45oC.
Considering you will not be using these valves to make any sound, the prices seem too high. You could consider the KT88 on the site you mentioned. They're as low as $44.00. WES sell a cheap KT66 for 37.50. There is no point in using a premium valve for your application. In fact, you should contact Lucas Miles and ask them if they have any faulty valves (but with functioning heaters) they can let you have cheap. Valves have a pretty high DOA figure. Probably in the order of 1 in 20 for Chinese valves. Russian ones are somewhat better. When I first started using Chinese valves, the DOA figure was around 50%. And, by DOA, I mean that the heater worked, but the rest of the valve was stuffed, on arrival, brand new, from the distributor. If Lucas Miles does a fair bit of work, then they'll see plenty of dead valves which you could use.
Don't forget: The KT66/KT88 runs much warmer than the 12AX7 I cited earlier. It will dissipate around 10 Watts of heater power. I'll try to measure the bulb temp later today, if I can find some time.
Usually, they're custom jobs.Last edited by Zaphod; 16th July 2009 at 08:49 AM. Reason: Brain fart
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16th July 2009, 11:23 AM #9.
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16th July 2009, 11:31 AM #10Senior Member
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Just to clarify: 45oC = 45 Degrees Celcius. It's not that hot, IMO (the human body operates at 38oC). That is the glass temperature. The surrounding air will be lower in temperature. If you can arrange some convection coooling, the glass temperature will be somewhat lower and the surrounding air temperature will be significantly lower.
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17th July 2009, 08:37 AM #11Senior Member
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17th July 2009, 11:11 AM #12
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