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| New Project - Direct coupled 845 SE amp. http://dcaudiodiy.com/phpBB3/viewtopic.php?f=4&t=1679 |
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| Author: | dberning [ July 13th, 2020, 11:26 am ] |
| Post subject: | Re: New Project - Direct coupled 845 SE amp. |
I don't know what the parasitic capacitance of the 100 H choke would look like, but if you have HF issues you might add a 1H choke in series. |
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| Author: | Roscoe Primrose [ July 13th, 2020, 11:31 am ] |
| Post subject: | Re: New Project - Direct coupled 845 SE amp. |
dberning wrote: I don't know what the parasitic capacitance of the 100 H choke would look like, but if you have HF issues you might add a 1H choke in series. This choke was specifically wound for plate choke use, but I'll keep that in mind. 1H chokes are easy  Roscoe |
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| Author: | ratbagp [ July 13th, 2020, 11:39 am ] |
| Post subject: | Re: New Project - Direct coupled 845 SE amp. |
dberning wrote: I don't know what the parasitic capacitance of the 100 H choke would look like, but if you have HF issues you might add a 1H choke in series. I've wondered about this. Would the 1 H choke make a 20H parafeed plate choke better if it is in series? ray |
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| Author: | SoundMods [ July 13th, 2020, 2:08 pm ] |
| Post subject: | Re: New Project - Direct coupled 845 SE amp. |
Roscoe Primrose wrote: SoundMods wrote: Roscoe Primrose wrote: Haven't built his yet, but it's next up in the queue... Roscoe Speaking of projects in the que -- did you ever build the tape-drive pre-amp you talked about? If you did -- how did it work out as compared to the stock electronics? Not yet. I did pick up a pair of late 60s Ampex solid state electronics, but haven't done anything with those yet either... Roscoe I expect they're no better than the electronics inside your tape decks. Very old school early SS. |
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| Author: | Roscoe Primrose [ July 13th, 2020, 2:25 pm ] |
| Post subject: | Re: New Project - Direct coupled 845 SE amp. |
SoundMods wrote: I expect they're no better than the electronics inside your tape decks. Very old school early SS. That's entirely possible. Of course, they're nice pretty chassis with meters etc. that I could use for my own circuits if the Ampex electronics don't cut it... Roscoe |
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| Author: | SoundMods [ July 13th, 2020, 3:21 pm ] |
| Post subject: | Re: New Project - Direct coupled 845 SE amp. |
Roscoe Primrose wrote: SoundMods wrote: I expect they're no better than the electronics inside your tape decks. Very old school early SS. That's entirely possible. Of course, they're nice pretty chassis with meters etc. that I could use for my own circuits if the Ampex electronics don't cut it... Roscoe Casework is one half of the battle -- why not keep the AMPEX electronics and find out what you really have by upgrading the critical-path passive parts? Ir it a tube piece or SS? Hunt down ceramic and/or silver-mica caps and replace them with WIMA pulse caps -- hunt down carbon composition resistors and replace them with Dale or Roderstein metal-film resistors -- hunt down critical path Aluminum or Tantalum electrolytics and replace them with WIMA stacked-film caps that are available in sizes up to 22-ufd that are hardly bigger than the little electrolytics they would replace -or- at least use Elna Cerafine or Silmic electrolytics. Any paper dielectric caps would have to go. If the piece has oil-filled caps in places that could work as-is. I've done a lot of that kind of work over the years and found that basic circuit design is usually very good in vintage equipment, but the parts choices available at that time left a lot to be desired. It just might surprise you. BTW -- I have a comprehensive inventory (maybe too damn many) of the very parts suggested including tubes. |
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