No- but you are leaving some voltage amplifier performance on the table. The original CCS of the circuit is 2-stage for a reason- if you implement a 2-stage solid state CCS of proper design it will perform better (including more gain).
If using 6C33s, a fuse in series with each tube is strongly recommended else heartache will occur.
If using 6C33s, a fuse in series with each tube is strongly recommended else heartache will occur.
Can you elaborate on this please.
Is there something special about the mig's - are they prone to anything?
Let's put it this way: if a 6C33 arcs, it will really get your attention 😡
Without a fuse on the tube, the arc can sound like a grenade. We find that 1.5 amp slow blow will do the job- its more current than the tube will see in service but if the tube develops an arc or a short, the fuse will blow quite readily.
Without a fuse on the tube, the arc can sound like a grenade. We find that 1.5 amp slow blow will do the job- its more current than the tube will see in service but if the tube develops an arc or a short, the fuse will blow quite readily.
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If you discharge a chemical with 150V on the speaker, that will give quite neasty plop!I have no practical experience with those russian tubes, but if you say so ...
And that doesn't happen with the 6AS7/6080 ?The more tubes in parallel the greater the risk I would think.
The better CCS for (also) more gain ? With the ECC86 (6mA/V) it is allready over 200x !
Mona
And that doesn't happen with the 6AS7/6080 ?The more tubes in parallel the greater the risk I would think.
The better CCS for (also) more gain ? With the ECC86 (6mA/V) it is allready over 200x !
Mona
If you really want a differential circuit to really work, a good CCS is the key. It cannot be accomplished with a single stage. The difference is very easy to measure BTW. I have to say I am constantly amazed at how many otherwise competent solid state designs I see and then they leave performance on the table due to a mediocre CCS.
You are not going to see 150V on the speaker! That would take a cathode/plate short which is really unlikely- in 39 years and 10s of thousands of power tubes I've yet to see that happen. Instead what you will see is grid/cathode arcs and shorts (which is dramatically reduced by preconditioning the tubes). With the 6AS7G the most likely result is that the fuse for the B+ transformer will blow if the tube persists with the short. That method is very good at protecting the speaker; if not we could not stay in business as with any tube amp, sooner or later a tube is going to fail. That is why they are in sockets and are user-replaceable 🙂
BTW we don't use driver tubes like that as we have a design policy called the '20-Year Rule' which states that the amp should be trouble-free for at least 20 years... to that end, we don't design to use tubes that are not currently available. I do concede that we broke that rule with our Novacron amp, which uses 6C33s. However that amp is a very limited run...
You are not going to see 150V on the speaker! That would take a cathode/plate short which is really unlikely- in 39 years and 10s of thousands of power tubes I've yet to see that happen. Instead what you will see is grid/cathode arcs and shorts (which is dramatically reduced by preconditioning the tubes). With the 6AS7G the most likely result is that the fuse for the B+ transformer will blow if the tube persists with the short. That method is very good at protecting the speaker; if not we could not stay in business as with any tube amp, sooner or later a tube is going to fail. That is why they are in sockets and are user-replaceable 🙂
BTW we don't use driver tubes like that as we have a design policy called the '20-Year Rule' which states that the amp should be trouble-free for at least 20 years... to that end, we don't design to use tubes that are not currently available. I do concede that we broke that rule with our Novacron amp, which uses 6C33s. However that amp is a very limited run...
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Hi,
Never seen that happen with 6080 or equivalent for over 30 years of use.
I occasionally pop a fuse though. Mostly when the amps haven't been used for months or so.
@Ketje: Wouldn't it be nice if you could swap out both ECC85 (even though EH still has it on offer) and the much harder to come by ECC86 with Russian 6N1-Ps?
I know the an ECC88 can run at such low B+ without any trouble at all.
And, yeah, those 6C33Cs need burning in to avoid trouble. After that they're great ugly bottles. 😀
Cheers, 😉
Never seen that happen with 6080 or equivalent for over 30 years of use.
I occasionally pop a fuse though. Mostly when the amps haven't been used for months or so.
@Ketje: Wouldn't it be nice if you could swap out both ECC85 (even though EH still has it on offer) and the much harder to come by ECC86 with Russian 6N1-Ps?
I know the an ECC88 can run at such low B+ without any trouble at all.
And, yeah, those 6C33Cs need burning in to avoid trouble. After that they're great ugly bottles. 😀
Cheers, 😉
To get 2mA with the ECC88 at 20V you need -Vg of 0.5V, to close to grid current.
Those ECC85/86 are not so hard to find 😉
Mona
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Ive had a 6C33C arc--and kill a speaker....
Strangely--The sounds were not huge. A nasty crackling/hum while the tube sparked and arced away....
--The speaker wasn't a huge loss, just a bench-speaker picked up at a S/H shop, rated at 50W and 8 ohm, 8" driver. The tweeter survived as was cap coupled....
Voice-coil was melted and burned, distorted and jammed in the magnet-airgap, but was not open circuit.
Since then, always fuses in each tube and another in feed to speakers!
6C33 arced because it was brand-new and Not burned in for long enough--It had only burned in for an hour or two, instead of at least 6 hours.
Strangely--The sounds were not huge. A nasty crackling/hum while the tube sparked and arced away....
--The speaker wasn't a huge loss, just a bench-speaker picked up at a S/H shop, rated at 50W and 8 ohm, 8" driver. The tweeter survived as was cap coupled....
Voice-coil was melted and burned, distorted and jammed in the magnet-airgap, but was not open circuit.
Since then, always fuses in each tube and another in feed to speakers!
6C33 arced because it was brand-new and Not burned in for long enough--It had only burned in for an hour or two, instead of at least 6 hours.
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@ Ketje , post # 87 , it's a good combination , a solid state CCS and a resistor , I had try in the past and the sound was realy good , empirical you can increase the value of R7 by 2 - 3 % to lower more the distortion , by the way ECC85 is one of my favourite tubes .
Hi,
When I was a kid you'd hardly find a radio set that hadn't at least one ECC85 in it.
Strangely enough it's not that popular in more modern designs. Even more strange to see it implemented in some Japanese designs a la the Taki OTL mentioned higher up.....
@Ketje: According to my old Philips databooks (you know, the "Gouden Gids sized ones) the ECC88 should not produce any grid current even when approaching Vg0 even at 2mA currents. IME it indeed does not.
Cheers, 😉
When I was a kid you'd hardly find a radio set that hadn't at least one ECC85 in it.
Strangely enough it's not that popular in more modern designs. Even more strange to see it implemented in some Japanese designs a la the Taki OTL mentioned higher up.....
@Ketje: According to my old Philips databooks (you know, the "Gouden Gids sized ones) the ECC88 should not produce any grid current even when approaching Vg0 even at 2mA currents. IME it indeed does not.
Cheers, 😉
Yes ! , you can find ECC85 in most FM tube radios , I use it in my OTL amps ( two amps one Futterman and one Circlotron , ECC85 and PCC85) and in the preamp too ! .
Guys sorry for off-topic but ....
Strange ,long time ago I have experimented with those ECC85 for some audio app., but 85 is basically UHF-RF tubes , and I never liked that narrow tinny metallic sound that they produce ,
microphony is another bad issue of those 85 , got bunch of them and I not planing to use them anywhere ever for audio
Strange ,long time ago I have experimented with those ECC85 for some audio app., but 85 is basically UHF-RF tubes , and I never liked that narrow tinny metallic sound that they produce ,
microphony is another bad issue of those 85 , got bunch of them and I not planing to use them anywhere ever for audio
Hi,
Never used them myself in any audio circuit but I know others that did. Mostly in amps though, as splitters mostly.
No idea what it sounds like to be honest.
You're quite right about them being intended for RF use but that does not say anything per se, right.
Cheers, 😉
Never used them myself in any audio circuit but I know others that did. Mostly in amps though, as splitters mostly.
No idea what it sounds like to be honest.
You're quite right about them being intended for RF use but that does not say anything per se, right.
Cheers, 😉
@ banat , Μy experience with the ECC85 is very different from yours , in my opinion ECC85 is a modified version of ECC81 , with a clean , wide and detailed sound , as for microphony , I find one in six tubes that have this problem , not too bad .
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Yes , clean and detailed sound but almost sterile as is some BJT`s ,
I have tried those 85 in some simple Mic pre ,and some preamp circuits with tone control and I was disapointed with the sound , never tried again those 85 for audio , but for some FM-RF-TX app. they are very very good 🙂
If you eventually refer for example on that Taki circuit where those 85 are used as diff. phase splitter ,my opinion is that is another mistake in that particular OTL circuit ,
two 6sn7 in that place will blow away with sound those two 85 🙂
Since I already have 109db horns 12ohm speakers I figured this would be a good opportunity to ask about tube OTL's. Never had the chance to try one. Any suitable, low cost circuit I should consider building so I'm not buying fancy stuff out of curiosity?
I think a good sounding design with 5-10watts would be a good start?
Herman
I think a good sounding design with 5-10watts would be a good start?
Herman
This one from Russia or China, don't remember where I found it, looks promessing.
Mona
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In the ECC88 data they messed up somewhat, better use the E88CC data.
A 90V 15mA the Vg is round -1V an allreay some grid current 😱
Mona
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The 6C33 should be run filament only, no B+, for at least 4 days and nights to precondition the tube prior to use. This is if the tube is unused since new. If you run it untested for 6 hours the likelihood of premature arcing is unchanged.
Ah- the low power OTL, a holy grail of sorts. One thing you will find is that OTLs make less higher ordered harmonics, so you actually wind up using the power they have as opposed to a SET. Because they don't make as much distortion, they don't sound as loud so you turn the volume up higher. That's a good thing BTW. The M-60 circuit I put up earlier can be executed with 2 or 4 power tubes- you don't have to use all 8 by any means! At home, because I don't like air conditioning, this year I have been running my M-60s with only 4 power tubes per channel; my speakers are 98 db and 16 ohms and I've really not noticed the loss in power. Haven't had to run the air all year too 🙂
We used to make a circuit like that which we discontinued in 1985. The problem with this driver was discussed earlier on this thread, to wit: even with hand-picked tubes, the circuit needs an AC balance means. The best place to put that is in the cathode of the first tube (balance potentiometer). It turns out though that this is poor means of balancing the circuit- it introduces as many problems as it solves. At best, the circuit does not come close to the cascode voltage amplifier we use, which is why we use the latter 😀 Take it from one who has experience with this- avoid that direct-coupled cascade. Looks good on paper but its doesn't work!
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