yeah, when i plug them in they blow a fuse. (why does it blow the fuse?) so i went out and bought ANOTHER one and the SS module which came with a slip stating this thing about a standby switch and cathode stripping due to quick rise in B+ voltage on a cold tube.
apparently this is not true though even wavebourne says so and also that one long thread about this matter here in this forum the link is posted above. so i dont think there is any need to make any mods.
when i use the tube i just have to wait a couple of minutes before i turn it on again after a shut down.
what does wavebourne say about those 1N4007s on the rectifier tube pins?
this is a triode electronics 2010 version of the st70.
You should always wait for the tube to cool down before restarting. The two simple mods I mentioned work pretty well, and if you don't like them for some reason, are easily removed without any damage to the amp and only cost a couple of bucks at most. I am wiring up the second of my 6L6 monoblocks today. They incorporate these two additions. Power comes up nicely, though I have not monitored/measured the current rise. The reason I have done these mods is because of reading (somewhere) that they work well in designs like the ST70 that place a high strain on rectifier tubes at startup. Looked like a good low-tech inclusion to improve tube reliability.
Cheers,
Chris
Cheers,
Chris
OK. Is that the whole shootin' match kit. Cap board, and all? Driver board, transformers, everything?
Before you use that SS rectifier, read the advisement in their advertisement about you telling them you want to go with the SS rectifier so they can upgrader the cap board with higher voltage rated caps to keep the SS rectifier from over spiking them.
yeah it's the whole high noon ok corral shootin' match
here is what they say in the ad -- Our ST70 Dynaco Upgrade Cap Board Replaces the original aluminium can capacitor and increases capacity from the original 30-20-20-20 to over 500uF's, using high quality capacitors which are bypassed by metalized polypropylene caps for superior high frequency response. This board gives the amp the bass definition the original lacked. Amp can be used with a 5AR4/GZ34 tube rectifier or solid state diode plug-in unit (sold separately), or just wire some diodes to the socket. It also replaces the bias supply capacitors & diode as well.
so i guess it's good to go with SS module.
what is the difference i should hear? maybe the sound is less rounded or something or am i imagining things. is it possible to hear the diff b/w solid state and tube rectification?
i guess i could have wired in some diodes but the empty socket would looked kinda weird.
sounds like a good idea ill keep it im mind.
do you have any theory on how that works? does it have to do with the time it takes before the diodes start to conduct?
6L6 monoblocks? cool. id like to see some pictures.
im wiring the miniblok with 13em7 for 1 watt of power. i finished one now just the other. this is the 4th time im rebuilding it. i think im content with it now. just need to get some more speaker posts. built some nice boxes for them with a little walnut veneer, spray painted the plate with speckled copper etc and they sound good. i use one for the center channel when i listen to Living Stereo SACDs that were originaly recorded in 1959/60 in three channels. it really sounds like you are in the concert hall on the first mezanine center (best seat in the house) lol fun hobby
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Go back and read a bit farther down, they added this a few paragraphs later...
Now, since you have the Triode PT that is supposed to have a beefier rectifier circuit, you can use a 5U4 type that has a higher voltage drop. You should be able to keep the '70 running with that so you can get some voltage measurements and time to think about the problem.
Now, since you have the Triode PT that is supposed to have a beefier rectifier circuit, you can use a 5U4 type that has a higher voltage drop. You should be able to keep the '70 running with that so you can get some voltage measurements and time to think about the problem.
wow thanks for the heads up on that! so the caps would need a higher voltage rating?
darn. things are never simple
thanks!
also i have the amp triode strapped so it is only running at about 15 watts rather than 35. do you think the capacitors are going to see a higher voltage with SS rectification? why would they see a higher voltage?
Cathode stripping IS a problem on DIRECTLY HEATED CATHODES, mostly... which are again mostly found (traditionally speaking) in RF and HV applications.
I see no reason whatsoever to let a tube "cool down" before turning the unit back on. What's the basis for that??
There is no reason not to put larger filter caps in the ST-70, IF the rectifier can handle the extra current, AND the power supply transformer can handle the extra current. I prefer to use the extra capacitance AFTER the little teeny tiny choke... fwiw. Works nicely.
Been doing ST-70s for a looooonnnnnggggg time.
The voltage on the caps problem comes when the tubes don't light up and DRAW current soon enough to draw down the peak voltage on the power supply - so you can exceed the peak voltage on the filter caps. That is something to look out for.
_-_-bear
I see no reason whatsoever to let a tube "cool down" before turning the unit back on. What's the basis for that??
There is no reason not to put larger filter caps in the ST-70, IF the rectifier can handle the extra current, AND the power supply transformer can handle the extra current. I prefer to use the extra capacitance AFTER the little teeny tiny choke... fwiw. Works nicely.
Been doing ST-70s for a looooonnnnnggggg time.
The voltage on the caps problem comes when the tubes don't light up and DRAW current soon enough to draw down the peak voltage on the power supply - so you can exceed the peak voltage on the filter caps. That is something to look out for.
_-_-bear
The voltage drop across a diode is usually <1v. while a tube rectifier like a GZ34 is @20v. A 5U4 tube drop is @50v. So the effective voltage out of the SS rectifier could be @ 30v. higher. The peak swing is even higher. Since those HV caps are bigger and cost more they (Triode) chooses to install them only when necessary.
this st70 has
2*82uF 400v
2*390uF 250v
4*270uF 250v
electrolytic caps in the cap board
does running the amp in triode mode affect the issue? are these voltages too low for the SS module?
this link for the cap board PSB
http://site.triodestore.com/ST70capinstructions.pdf
so the issue is not with the electrolytic filter caps then? i have next to no understanding of the circuit of this amp. i just put the pieces together when i didnt even know what a tube was or how to read resistor values. it's a miracle i didnt destroy the output transformers but im picking up knowledge and experience slowly.
i should try studying the schematic of this thing
i posted a link to the cap board
can you advice which caps to replace with what values?
thanks
why bother?
GZ34/5AR4 is still in production. Why bother with solid state? Lots of arguments for/against damage from instant B+, my opinion is 4 each 6CA7 costing $120 a set is worth a little "needless" protection. I recently bought a new Sovtek tube, worked fine in my Hammond H-100 organ, which has more capacitance on the tube and more load, than the ST70. If you're still running OEM 7199 tubes, they are unobtainable. My 7199's have lasted 49 years with tube rectification, why experiment? Do the experiments on transistor amps where you can buy the parts.
GZ34/5AR4 is still in production. Why bother with solid state? Lots of arguments for/against damage from instant B+, my opinion is 4 each 6CA7 costing $120 a set is worth a little "needless" protection. I recently bought a new Sovtek tube, worked fine in my Hammond H-100 organ, which has more capacitance on the tube and more load, than the ST70. If you're still running OEM 7199 tubes, they are unobtainable. My 7199's have lasted 49 years with tube rectification, why experiment? Do the experiments on transistor amps where you can buy the parts.
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Slow start is not a "needless" protection. It charges capacitors by smaller current; it does not cause such a stress to grids of tubes like standby switch, or delay relay, does. Look what happen to control grids of hot tubes when B+ switches on abruptly, while coupling capacitors are still discharged!
By the way, I don't use anymore thermistors to reduce inrush currents: 18 Ohm wirewound resistor in series with primary works better. Relay powered from filament rectifier shorts that resistor deadly.
By the way, I don't use anymore thermistors to reduce inrush currents: 18 Ohm wirewound resistor in series with primary works better. Relay powered from filament rectifier shorts that resistor deadly.
It looks like the two 82mf caps are in series and that reduces the capacitance to 41mf. If they are in parallel its 164mf.
The GZ34 data sheet lists the max recommended for the caps to be 60mf. And with 60mf the sheet recommends 2 100R current limiting resistors between the transformer and the tube.
The original '70 uses 30mf of input capacitance and doesn't blow tubes or fuses. I'd email Triode and tell them you can't keep a rectifier in it and maybe they would tell you to send them the board and they would update it. Or at least send you some other caps so you could do it. BUT, I think your problem is all about too much capacitance creating a giant surge through the tube and your fuses.
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Because the new GZ34s have a reputation for dying. SS rectifiers are more reliably long lived, can tolerate larger capacitance, and there are no arguments against damage from instant B+. SS rectifiers do not cause large voltage loss, B+ 'sag', or require a heater winding. And if you do want sag and a soft start you can duplicate a GZ34 with a big resistor, at a fraction of the cost.
Word fail me.
Ok, not all words: It is hardly experimentation. Tube amps have been running SS rectifiers since the 60s. It is the valve rectified ones that are now in the minority!
HI Wavebourn i have not look at grid but ,as I have on the same trafo the AC heaters ,ss b+ ,fix bias ,the bias drop some volts when the delay b+ relay hit!! (the fix bias have separate diode/caps/secondary coils)
very bad , to have all tension on the same trafo and solid state diode , I don't know if ss or tube sound better , probabily ss have better bass but tube without switch noise can be more musical.... sure the psu impedence is different.
for what i reads ,with a good system a tube diode sound magic ,better if have mesh plate , 30ohm choke ,pp motor run caps.
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When I bought my ST70 it was producing 20 watts because the rectifier, 6CA7's and B+ cap were tired, according to the Macintosh guy. Upgrading all that was just barely audible. Because of the logrithmic nature of ear response, the difference between say 425 v B+ and 450 v B+ is in the tenths of a db area. If you're worried about that, buy or build more efficient speakers.
Some experts say ss rectification doesn't hurt, other experts say it does. Other threads go on ad naeum about this. The sovtek 5AR4 is $18, small change even to the unemployed. The risk of a modern tube recitfier is a shortout and burning the power transformer. So put a "fuse" in between the transformer and the rectifier and address the issue directly. Because you can't buy 200 ma fuses in the 600 VDC rating, I put a header in my organ and put the finest strand wire teased out of a 20 gauge between two terminals- about 1/2" for voltage separation. That is in series with the HT winding on my organ. If a tube shorts out I'll let everybody know how the experiment worked. So far 7 months, no issues.
The capacitance of your ST70 in series with the rectifier seems to be a bit high. OEM is 40-20-20-20. Hammond puts about 300 uf on a 5AR4 in the H100 organ, the rectifiers last about twenty years. (according to the box on the replacement left in my used organ) 200 uf of that capacitance was in remote chassis at the end of 6' of 20 gauge wire. See the H100 Hammond service manual on archive.org Fig 41 upper right.
I did put dual 50 uf motor starter (film) caps in my organ instead of electrolytics. I had to build a separate chassis to cover the terminals from humans. The bass on the organ is amazing, knocks the tubes right out of the sockets with the pedal full down.
Some experts say ss rectification doesn't hurt, other experts say it does. Other threads go on ad naeum about this. The sovtek 5AR4 is $18, small change even to the unemployed. The risk of a modern tube recitfier is a shortout and burning the power transformer. So put a "fuse" in between the transformer and the rectifier and address the issue directly. Because you can't buy 200 ma fuses in the 600 VDC rating, I put a header in my organ and put the finest strand wire teased out of a 20 gauge between two terminals- about 1/2" for voltage separation. That is in series with the HT winding on my organ. If a tube shorts out I'll let everybody know how the experiment worked. So far 7 months, no issues.
The capacitance of your ST70 in series with the rectifier seems to be a bit high. OEM is 40-20-20-20. Hammond puts about 300 uf on a 5AR4 in the H100 organ, the rectifiers last about twenty years. (according to the box on the replacement left in my used organ) 200 uf of that capacitance was in remote chassis at the end of 6' of 20 gauge wire. See the H100 Hammond service manual on archive.org Fig 41 upper right.
I did put dual 50 uf motor starter (film) caps in my organ instead of electrolytics. I had to build a separate chassis to cover the terminals from humans. The bass on the organ is amazing, knocks the tubes right out of the sockets with the pedal full down.
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My ST70 has more capacitance than stock. I arced over my rectifier a few times before doing the UF4007 diode mod. It was also the subject of one of my first posts to this forum. 🙂 Later I added a CL90 to the mains, which stopped the angry transformer *clunk* at powerup. I've had the same JJ GZ34 in there since and it has been working great. I thought about adding a CL150 in series with the first cap, but I haven't seen the need with the tube rectifier.
Oddly I still have that Chinese 5AR4 that arced over several times in this amp. It still works fine for some reason. I use it in new amps. It's been in my SimplePP for a while now.
Oddly I still have that Chinese 5AR4 that arced over several times in this amp. It still works fine for some reason. I use it in new amps. It's been in my SimplePP for a while now.
30-20.....
Some other questions to be answered about the power supply are,
(1) Is the DCR of the new PT's as high as the original? If not then that adds to the surge.
(2) Is the DCR and inductance of the new choke as high as the original Dynaco's? If not then also adds to the surge. Even a 5% difference is enough to tip the scale if the input capacitance is higher, pulling more than designed and if one of those new fangled GZ34 is used, too.
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