Hi Shoog, I have the toroidal mains transformer now for OPT, I have the interstage for phase inversion.
Am thinking of using 5670 SRPP for the driver, would this work?
Am thinking of using 5670 SRPP for the driver, would this work?
With a 1.35W diss I don't like the look of it really. There are few valves up to the job really. The 5687 is a champ and could be configured for SRPP duty for even better performance.
Did you pick up that I am now running my interstage as a centre tapped choke rather than a straight transformer. Lower interwinding capacitance and better top end response.
One thing I have considered trying was moving the interstage to the front and then configuring a pair of 5687's as a LTP.
Shoog
I just had a major system crash which took out all of my hard drive, so I haven't got it. If you trawl back through this thread you should see a version and I can correct any differences.
Shoog
Shoog
18v will infact be good for 8ohms speakers
I use 4Ohm speakers and I unwound my toroidals to 11V.
Sorry for the confusion.
Shoog
Your right on the button with the ratio's.
Thats not the schematic, I replaced the ECL82 front end with 5687. I also configured the interstage as a CTC and increased the parafeed cap to 4uf. Also the secondaries of the interstage need loading with a 100K resistor to stop ringing.
The frequency response is good but a little rolled off at the top end - this is the fault of the interstage rather than the output transformer. Response is down to 10hz. The roll off is pleasing rather than annoying.
Shoog
Thats not the schematic, I replaced the ECL82 front end with 5687. I also configured the interstage as a CTC and increased the parafeed cap to 4uf. Also the secondaries of the interstage need loading with a 100K resistor to stop ringing.
The frequency response is good but a little rolled off at the top end - this is the fault of the interstage rather than the output transformer. Response is down to 10hz. The roll off is pleasing rather than annoying.
Shoog
The whole point of my project was to implement an interstage transformer on the cheap. It has worked out extremely well and for me the interstage transformer approach is a proven winner. When I feel flushed I'am going to invest in some Lundahl LL1660 to upgrade.
I like the look of that driver arrangement. It combines a SE input stage which will introduce a slight bit of 2nd harmonic for warmth, along with a LTP for accurate powerful phase splitting. Should work very well with probably better top end response. Won't be a lot in it cost wise though.
My last two projects have used input transformers for phase splitting, driving both inputs of of a LTP. This preserves the gain of the LTP (full gain of the triode as apposed to half gain with only one input driven) and has most of the benefits of the transformer phase splitting. In one project I have used a step down toroidal mains transformer at the input with no frequency penalties.
Shoog
I like the look of that driver arrangement. It combines a SE input stage which will introduce a slight bit of 2nd harmonic for warmth, along with a LTP for accurate powerful phase splitting. Should work very well with probably better top end response. Won't be a lot in it cost wise though.
My last two projects have used input transformers for phase splitting, driving both inputs of of a LTP. This preserves the gain of the LTP (full gain of the triode as apposed to half gain with only one input driven) and has most of the benefits of the transformer phase splitting. In one project I have used a step down toroidal mains transformer at the input with no frequency penalties.
Shoog
I am a complete noob on tube amps and hope that you guys can further enlighten me,
I want to build a 6080 pp amp (have the tubes already) but there is so much info here that I cannot decide on a design.
Shoog's looks promising but I do not understand the remarks on changing the interstage transformer to a centertapped choke, what does that mean?
I can buy some toroids for the opt"s but they are rather smallish 40VA's. what currents are you seeing in the primaries? are these going to be too small?
if possible I would like to use the other tubes I already have but that may be to much to ask, I have a nice mullard e88cc and some good ecc35's
Any help to get me on the way is appreciated!
I want to build a 6080 pp amp (have the tubes already) but there is so much info here that I cannot decide on a design.
Shoog's looks promising but I do not understand the remarks on changing the interstage transformer to a centertapped choke, what does that mean?
I can buy some toroids for the opt"s but they are rather smallish 40VA's. what currents are you seeing in the primaries? are these going to be too small?
if possible I would like to use the other tubes I already have but that may be to much to ask, I have a nice mullard e88cc and some good ecc35's
Any help to get me on the way is appreciated!
Hi there,
To answer some of your questions.
First off 40VA for the outputs are a little low for my taste, but i am currently using something similar in a headphone amp which is just about up to driving my main speakers with reasonable bass. I would say go with it and report back.
There are two issues with this design which I feel I must point out before you embark on it. Firstly getting a suitable power transformer is quite an ask. Something like an Isolation transformer might do, but then you will need a seperate heater transformer. Secondly though the amp was always loved and well received by others, it always had a slight bit of high frequency roll off - which came from using a toroidal as the interstage. It worked but the design calls for huge primary current to overcome the interwinding capacitance (which bleeds off the top end) . Really these tubes deserve a decent real interstage transformer such as the Lundahl LL1660, and if i was to rebuild I would use these. This would then definately make it a competition winner. The instage transformer is the most difficult transformer to design and so it costs money.
I have had recent success with moving the phase splitting transformer to the front end and using LTP from there on. I attach a concept schematic to show you what I mean, but I would be inclined to modify it slightly before going ahead and building it.
The best thing about this amp is the operating point of the finals 100V,100mA works really well - also the differential output stage is essential when using toroidals as output, which again work amazingly well.
Shoog
To answer some of your questions.
First off 40VA for the outputs are a little low for my taste, but i am currently using something similar in a headphone amp which is just about up to driving my main speakers with reasonable bass. I would say go with it and report back.
There are two issues with this design which I feel I must point out before you embark on it. Firstly getting a suitable power transformer is quite an ask. Something like an Isolation transformer might do, but then you will need a seperate heater transformer. Secondly though the amp was always loved and well received by others, it always had a slight bit of high frequency roll off - which came from using a toroidal as the interstage. It worked but the design calls for huge primary current to overcome the interwinding capacitance (which bleeds off the top end) . Really these tubes deserve a decent real interstage transformer such as the Lundahl LL1660, and if i was to rebuild I would use these. This would then definately make it a competition winner. The instage transformer is the most difficult transformer to design and so it costs money.
I have had recent success with moving the phase splitting transformer to the front end and using LTP from there on. I attach a concept schematic to show you what I mean, but I would be inclined to modify it slightly before going ahead and building it.
The best thing about this amp is the operating point of the finals 100V,100mA works really well - also the differential output stage is essential when using toroidals as output, which again work amazingly well.
Shoog
Attachments
Wow - what would a fella have to do to get a copy of that "handy reactance chart". Ima hopeless newbie - but I know a vein of gold when I hear one.
Since this thread has popped back up again i will tell everyone whats the situation with my amp. I gave it away to my Dad and moved onto the Tabor clone.
Still I have been in contact with a man in Canada who built the amp as shown in this thread, he was really impressed saying it was better sounding than any of the high price commercial amps he had heard. His friend borrowed it and wont give it back. He's building another version with LL1660's as the interstage - which allows him to drop the CCS on the driver. Hopefully when he finishes he will tell me how it performs.
I am currently working up to building a second version of this amp. The line up will be, a mains toroidal for the front end - with a step down of 2:1+1. A LTP driver made from the dual pentode 12L8GT hanging off a negative rail of -180V. This will be direct coupled to the 6080 which will be unchanged. I will use TL783's for the cathode CCS, as they are rated at 125V and have better performance characturistics than the LM317. The higher voltage is important in direct coupling because the voltage's do weird things on power up and tend to burn out wimpy CCS's. The direct coupling will allow for a little local feedback which will further lower the output impedance.
this is basically what I suggested in my last schematic - but with pentodes as drivers.
I anticipate this version to have better high frequency extension and tighter bass. I will lash up a schematic in the next few days and post it up for consideration.
Still I have been in contact with a man in Canada who built the amp as shown in this thread, he was really impressed saying it was better sounding than any of the high price commercial amps he had heard. His friend borrowed it and wont give it back. He's building another version with LL1660's as the interstage - which allows him to drop the CCS on the driver. Hopefully when he finishes he will tell me how it performs.
I am currently working up to building a second version of this amp. The line up will be, a mains toroidal for the front end - with a step down of 2:1+1. A LTP driver made from the dual pentode 12L8GT hanging off a negative rail of -180V. This will be direct coupled to the 6080 which will be unchanged. I will use TL783's for the cathode CCS, as they are rated at 125V and have better performance characturistics than the LM317. The higher voltage is important in direct coupling because the voltage's do weird things on power up and tend to burn out wimpy CCS's. The direct coupling will allow for a little local feedback which will further lower the output impedance.
this is basically what I suggested in my last schematic - but with pentodes as drivers.
I anticipate this version to have better high frequency extension and tighter bass. I will lash up a schematic in the next few days and post it up for consideration.
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Hi Shoog,
I have a pair of Lundahl 1660S and am about to order some Talema toroidal for OPT, 225VA good enough?
Thanks.
I have a pair of Lundahl 1660S and am about to order some Talema toroidal for OPT, 225VA good enough?
Thanks.
Is the LL1660S the one that capable of standing DC. If so then the whole design takes on a degree of elegant simplicity that just looks and feels right.
As for the OT, a bit overkill really 😀 Anything above 50VA should work. Mine have all been Telema 120VA.
Shoog
Edit: come to think of it that LL1660s is totally unsuitable - send it to me for disposal.
As for the OT, a bit overkill really 😀 Anything above 50VA should work. Mine have all been Telema 120VA.
Shoog
Edit: come to think of it that LL1660s is totally unsuitable - send it to me for disposal.
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I still have the Lundahl 1660S on my EL84 PP, I will be rewiring that EL84 PP so that I can free my LL1660S.
Thanks for the info.
The shipping to your country will be prohibitively expensive, I will just throw in in the Pacific Ocean for disposal.
Careful -- there is a LL1660S/PP (push-pull) that is only gapped for a few mA offset. The "S" means that it's a "Splitter" transformer, not necessarily SE in this case. The ones gapped for DC are LL1660S/10 (for 10mA) etc.
From the data sheet"
"LL1660S is a version of LL1660 with internal Faraday shields to improve balance in phase splitting interstage
applications. The transformer is available with different core air gap for different driving tubes." The data sheet shows options for SE or PP gap.
So if you really can't use them, I'll pay shipping to my doorstep ;-)
Cheers,
Michael
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The LL1660S can also be used for SE - SE operation like the LL1660, the "S" stands for shielded.
I have used it up to 20ma current on the primary with great results, the specs said no more than 50ma per section. I have used it as an interstage for a 6n1p-2a3 SE amp and now for a EL84 driving an EL84 PP stage as phase inverter. 😀
Now, I will be using it for a 6080 PP. 😀
I have used it up to 20ma current on the primary with great results, the specs said no more than 50ma per section. I have used it as an interstage for a 6n1p-2a3 SE amp and now for a EL84 driving an EL84 PP stage as phase inverter. 😀
Now, I will be using it for a 6080 PP. 😀
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