Finished an OTL and now thinking tube substitution
This thread got me inspired to finished my OTL project that I started 8 years ago and 7 house moves later. Its a Transcendent T8 OTL schematics that Bruce Rozenblit published in his book. The amp sound very similar to a Futterman H3aa I used to have ...but has a much better bass.
I gotta give Ralph OTL circuit a try in the near future... The circuit looks so elegant and sublime.
My question is what Tube substitution that may work:
The Russian EL509 are getting expensive and out of 19 tube I got from ebay 3 were bad.
The measurement for my tube tester shows the actual spec are not really that tight.
I'm thinking about using 6C41C ... They are not as expensive, no top cap and looks cool.
The EL509 are configure as a Triode ...Plate is 170v Bias -40v
I'm thinking ... just change the bias -70v. Max plate dissipation is 35watt for the EL509 and 30watt for the 6C41C.
Any comments of the 6C41C in term of tube consistency, ruggedness and sound quality ?
Any tips ...like Preheat the heater for a few day
Any other sweep tube that are plentyful ? I see alot 6P42S on ebay
I've tried the 6C33C ... but found the bias wandered a bit and ran scary hot.
Thanks in advance
This thread got me inspired to finished my OTL project that I started 8 years ago and 7 house moves later. Its a Transcendent T8 OTL schematics that Bruce Rozenblit published in his book. The amp sound very similar to a Futterman H3aa I used to have ...but has a much better bass.
I gotta give Ralph OTL circuit a try in the near future... The circuit looks so elegant and sublime.
My question is what Tube substitution that may work:
The Russian EL509 are getting expensive and out of 19 tube I got from ebay 3 were bad.
The measurement for my tube tester shows the actual spec are not really that tight.
I'm thinking about using 6C41C ... They are not as expensive, no top cap and looks cool.
The EL509 are configure as a Triode ...Plate is 170v Bias -40v
I'm thinking ... just change the bias -70v. Max plate dissipation is 35watt for the EL509 and 30watt for the 6C41C.
Any comments of the 6C41C in term of tube consistency, ruggedness and sound quality ?
Any tips ...like Preheat the heater for a few day
Any other sweep tube that are plentyful ? I see alot 6P42S on ebay
I've tried the 6C33C ... but found the bias wandered a bit and ran scary hot.
Thanks in advance
Attachments
The 6C41 should work fine if you have enough of them! You should be able to use it in the schematics shown in this thread, with only minor changes in the bias to accommodate the tube. It seems to have a lower Rp than the 6C33 so IMO it is better suited than the 6C33, although you will have to use more of them. I'm thinking 6 of them should make about 60 watts, but unlike the 6C33, the socket will hold up for decades.
Hi
That is maybe because it is not technicly (?) possible? I remember when i was repairing tv in the past, philips were using 800 ohm speakers with el86 as far i remember! So maybe if we could get 800 ohm speakers....or 400... or 200 ?
To avoid many tubes in paralell . So the solution is in the SPEAKERS !
Paralleling tubes does not seem to be any more a problem for an OTL as it is for any larger transformer coupled amp, or for that matter a higher power transistor amp, except the OTL sounds a whole lot better
Back in the old days, there was a tube called the 7241. A pair of them could make 60 watts into 8 ohms, two pair can do about 150 watts. They take a 7-pin Septar ceramic socket, slight different but the same size as what is used with the 6C33 (a pair of those into 16 ohms will do about 25 watts BTW).
I really don't see any advantage to a super high impedance speaker as the voice issues become profound, and there does not seem to be a real need. IMO the only thing in that regard that does not make sense to me for good sound is 4 ohms. Its good for public address because you can make more power if you have transistors, but even a transistor amp will sound better driving 16 ohms than it will on 4, all other things being equal.
Unless you want to make a really low power OTL, there is no point in going over 32 ohms.
With 4 6AS7Gs you can make nearly 60 watts into 32 ohms as long as you increase the B+ slightly to accomodate the higher load impedance. I have used a line array to create a 32-ohm load in a guitar combo amp driven by such an amp. It worked great!
Jim,
Looks like Pin 4 for the plate of the 6C41
http://www.tkhifi.com/datablade/6c41c.pdf
what do you think ?
Looks like Pin 4 for the plate of the 6C41
http://www.tkhifi.com/datablade/6c41c.pdf
what do you think ?
Jim,
I had to look it for myself ... I'm building an adapter for my tube tester to test about 20 of them. I want to know how consistent the group of tubes are to each other.
If tubes are consistent, I will build a new totem pole output stage for my OTL.
What are you going to build with yours ?
I had to look it for myself ... I'm building an adapter for my tube tester to test about 20 of them. I want to know how consistent the group of tubes are to each other.
If tubes are consistent, I will build a new totem pole output stage for my OTL.
What are you going to build with yours ?
If its any help, I did a lot of that experimentation already. At least in the case of the 6AS7G, if you have a gutsier driver, it wins you maybe another watt. With the 6C33 it would not even win you that; the 6C33 has an almost pentode-like saturation compared to most triodes. IOW that 6SN7 CF driver is **already** set up for class A2 and works really well.
6as7
Be wary.
I ordered eight Sovtek NOS 6AS7 from the Ukraine on Ebay. They were anything but! 5 tested bad. And three passed at the bare minimum. These were all used. I guess you pay less and get less. As they were only $48.00 for all eight. Bottom line I should have know better then to buy some thing from Russia.... I am waiting to see if they will refund me. If not its still covered under Ebay buyer protection. There are quite a few sellers on Ebay from Russia or X parts that use to be under their control. With nice prices as well. But, I would say its too good to be true.... Buy, them from someone in the US that tests them. And them test them yourself no matter who you get them from!
Be wary.
I ordered eight Sovtek NOS 6AS7 from the Ukraine on Ebay. They were anything but! 5 tested bad. And three passed at the bare minimum. These were all used. I guess you pay less and get less. As they were only $48.00 for all eight. Bottom line I should have know better then to buy some thing from Russia.... I am waiting to see if they will refund me. If not its still covered under Ebay buyer protection. There are quite a few sellers on Ebay from Russia or X parts that use to be under their control. With nice prices as well. But, I would say its too good to be true.... Buy, them from someone in the US that tests them. And them test them yourself no matter who you get them from!
Ebay is always caviat Emptor. However that said, I have bought over 400 tubes so far with only a few bad, and three broken in shipment. The broken ones were replaced. The bad ones I didn't find till much later, and all but one may be due to damaging the amp with the first bad one.
Sorry to hear you got a lot that was bad.
Sorry to hear you got a lot that was bad.
I brought bunch of tube from the Ukraine and Russia on ebay from 3 separate vendor. I just had bad experience from one vendor who no longer sell tubes... The 12 "new" tubes (EL509) were pull out from some equipment ... the top cap fell off due to heat. He quickly disappear from ebay. The 2 other vendor was very professional and had no transaction issues.
I had a bad experience from tube seller from China ... I got emails stating that he was in a car accident ... then needed surgery.... please be patient ... Never got the tubes ....The time elapse(90 day?) to long for ebay to do anything about it. While all this time he was putting new stuff to sell on ebay...
You have to know the good sellers
I had a bad experience from tube seller from China ... I got emails stating that he was in a car accident ... then needed surgery.... please be patient ... Never got the tubes ....The time elapse(90 day?) to long for ebay to do anything about it. While all this time he was putting new stuff to sell on ebay...
You have to know the good sellers
This is a well-known scam, mainly used by chinese sellers of various items (I haven't had anybody else try to pull it off on me). Paypal will only let you to file dispute within 45 days of auction ending and eBay will only let you file negative feedback (which won't get your money back but it would warn future buyers about the scam) in 60 days after auction ends.
There is no 90-day deadline.
If you want your money back, file your disopute within 45 days, do not let the seller delay you past 45-day deadline with silly excuses.
I've seen a lot of 6AS7Gs that test poorly on emissions testers that run fine in the circuit. Most tube testers test the tube as a diode rather than a triode as the mu is so low. As a result they often don't give you a decent reading.
I'm looking at different transformers for the DIY M60 .... Is there a preference for a Toroidal type transformer for the output section ?
I'm going to implement this neat Heater / HV switch arrangement on my DIY Rozenblit OTL ... and Hopefully soon the DIY M60
The defunct "Sound Practices" mag allows for reproduction of its non copyrighted material
I'm going to implement this neat Heater / HV switch arrangement on my DIY Rozenblit OTL ... and Hopefully soon the DIY M60
The defunct "Sound Practices" mag allows for reproduction of its non copyrighted material