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I've read on several web sites that removing the recifier tube with diodes would result in more listening fatique, loss of vintage and tube like sound and several other reasons that I forgot why not to do it.While others say the recifier removes sag and voltage drops at lower frequencies restoring full listening spectrum.
My main concern is listening fatique, keeping sound quality and detail for long classical listening and occasional LOUD rock n roll.
Any help would be appreciated
Charles
Follow Ups:
From what I can gather you "clean" up the sound and lose the sound at the same time. So the majority seems to favor leaving the recifier tube alone. It's a done deal the tube stays. How does the Phillips tube sound in these units.
Charles
The stereo 70 with the tube rectifier has a sense of magic to it.Some people claim that if you like this sound that you`re deaf.Others feel that the amps accumulation of errors and comprimises account for this *sound* and that it must be *fixed* especially where the rectification is concerned.I`ve found that replacing the tube with SS strips this amp of any relative musical quality it had in the first place and that you`re left with a pale remnant of an amp that was somewhat special sounding under the right circumstance.I say leave it alone.Dynas don`t rock with any kick anyway.Like myself and many others have,you can toil endlessly in an attempt to make this amp do things it just doesn`t want to do by modding it up.In the end I`ve found that there are other amps that do naturally what you wish the Dyna might do when modded.This amp can do what it does right when it`s close to stock and ultimately not much more.If you want to rock vintage style,get a Citation II,wire KT90s in triode,and you`re done.At least the Citation has a sense of weight and energy,even when played at low volumes.Good Luck
If I were concerned about listener fatigue, then I wouldn't get anywhere near a solid state device. If you replaced the GZ34 with diodes, then the B+V would rise considerably. It would have much noise floor trash (spike hash) in it from silicon rectification. The existing choke and caps will not completely clean this up. About the only place it would benefit to use a single 1n4007 is the bias supply. Yes there are hexfreds but they require heat sinking and still aren't as good as a tube rectifier. If you're concerned about cost of the rectifier, then there are damper diode tubes you could convert to (many varieties just sitting on the shelf & cheap). The only problem is that you have to use two. The best! James
Alan Kimmel ST-70 mod is the best I have heard as far as ST-70 mod. His design leave the tube rectification alone. I listened to some ST-70 mod putting a solid state rectifier to replace those tube rectification. The result is "loss of magic"!! So why bother the ss rectifier on the ST-70.
My recommendation would be to buy a plug in diode rectifier and give it a try. They can be had for about $10 or you can make one yourself for the cost of two diodes.Your B+ will shoot up a bit and you'll hit max voltage very quickly unlike with a tube rectifier. I tried it and really, really, really didn't like it.
John
Charles,I've seen many guitar amps which had a couple of SS diodes soldered to the rectifier's lugs AND the tube recitifer still in place. I suppose this is to get some of the benefits of both worlds. To me, the tube rectifier's "spongy" attack or sag is lost---so why not just replace it with a complete SS recitification, if more bass or loudness is what you what?
For playing six-string guitar, you kinda want the amp to pump or "breathe" which the tube rectifier allows. But, for use in hi-fi perhaps the SS-rectifier is better, since there is less sag and therefore less overall distortion.
BTW---all of the amps I've seen with SS diodes replacing OEM tube types have had blown filter caps. Like John said the B+ (and other VDC) will go up and be instantaneous---so probably best to change the first filter caps perhaps to two caps, in parallel, with higher capacitance at a healthy voltage rating (like 400 volts).
Gerald Weber suggests two 220 mfd, 350 volts caps in parallel to replace the OEM two 70 mfd caps, in a tweed Fender Bassman. 220 K, 2 watt resistor across the two caps to divide the voltage evenly. Then, the first set of caps would have a total filtering capacity of 110 mfd with a 700 volt rating.
As others have already stated (or implied), replacing the 5AR4 with SS rect will raise the PS output voltage considerably. In the case of the ST70, you will most likely exceed the safe operating voltage of the filter caps. This is especially true considering that in most localities in the US at least, the mains voltage is now routinely 120+VAC compared to the nominal 117VAC when the ST70 was current. If you want to experiment with SS rect you need to up the voltage rating of the PS caps. One way of doing this is to put two identical caps in SERIES, not parallel as stated above (a slip of the keyboard, I'm sure). The cap will divide by 2 in value while the voltage rating will double. The resistors can be placed in parallel across each cap in series to equalize voltage drop. Another way to do this is to get the SDS labs cap board kit from triodeel, a sponsor.BTW I'm not steven oda but yet another Steve O.
Steve,Thanks, for the clarification.
steve
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