i built for a friend this double PP of 6550 100+100Watts rms
the particularity is that all the connections between the tubes are made in direct coupling and/or by inter-stage transformer.
on this amp I do not use transistors but conventional resistor biasing, and all stages are direct coupled
it's very rare these days I don't know of any commercial amp with this feature
in the good old days it was used for class AB2 professional amps of several hundred or even thousands of watts
input on transformer 1:0.5/0.5 high impedance 40K/20+20Kohm
first stage amplification E80CC audiogold cathode resistor non-polarized cathode capacitor 47uF 100V
followed by a buffered 6SN7 cathode follower i forget small neon lamp grid cathode
but HT switch allow tubes heat up
then a 6SNTWGT Sylvania brown base in differential inter-stage transformer driver 1/1:1/1
finely tuned with symmetry fine tuning.
in the secondary a last 6SN7 Foton in buffer and bias management to drive the double PP of 6550C svetlana.
each 6550C is fitted with a 10H 7W wire wound cathode resistor
res screen G2 1K 7W wound wire ultralinear assembly
res grid 1 2K2 ohm 2W wound wire
each phase individual bias settings
all these stages in direct connection no caps without feedback (feedback)
the particularity is that all the connections between the tubes are made in direct coupling and/or by inter-stage transformer.
on this amp I do not use transistors but conventional resistor biasing, and all stages are direct coupled
it's very rare these days I don't know of any commercial amp with this feature
in the good old days it was used for class AB2 professional amps of several hundred or even thousands of watts
input on transformer 1:0.5/0.5 high impedance 40K/20+20Kohm
first stage amplification E80CC audiogold cathode resistor non-polarized cathode capacitor 47uF 100V
followed by a buffered 6SN7 cathode follower i forget small neon lamp grid cathode
but HT switch allow tubes heat up
then a 6SNTWGT Sylvania brown base in differential inter-stage transformer driver 1/1:1/1
finely tuned with symmetry fine tuning.
in the secondary a last 6SN7 Foton in buffer and bias management to drive the double PP of 6550C svetlana.
each 6550C is fitted with a 10H 7W wire wound cathode resistor
res screen G2 1K 7W wound wire ultralinear assembly
res grid 1 2K2 ohm 2W wound wire
each phase individual bias settings
all these stages in direct connection no caps without feedback (feedback)
Interesting small monster. I also made an audio amp with compactron tubes all DC coupled with series pushpull (OTL) but l keep it still a prototype, unfinished.
It's a pretty interesting challenge to make tube DC coupled without one ss device.
It's a pretty interesting challenge to make tube DC coupled without one ss device.
thanks Osvaldo de Banfield, input splitter transformer and driver transformers help a lot , this amps was built 6 months ago and still working, no problems
My only suggestion would be to add a large np cap across the last 6SN7's cathodes in order to help counteract any AC umbalance. IMO a great design. Enjoy.
At most this design avoids "capacitor sound" issues :-/
At most this design avoids "capacitor sound" issues :-/
the last 6SN7's cathodes go directly to 6550C grids resistors!its a CF direct coupled driver stage capable of many multipair output tetrodes
Great job. I like your UL approach with no global NFB. What is the output impedance? What kind of speakers you are using with your amplifier?
I see that you are loading the secondaries of your input and interstage transformers. IMO, this is not necessary, unloaded transformers sound better.
What is your interstage transformer?
Is there any reason for using different brands of 6SN7 tubes in different positions?
I see that you are loading the secondaries of your input and interstage transformers. IMO, this is not necessary, unloaded transformers sound better.
What is your interstage transformer?
Is there any reason for using different brands of 6SN7 tubes in different positions?
loading the secondaries of input and interstage transformers its fondamental for stability linearity and thd
input 560Q and predriver 124F both Hammond
using different brands of 6SN7 tubes in different positions come from my sensibility and experience
6SNTWGT Sylvania recommended for heather cathode insulations
OTP its 1650T 1K9
input 560Q and predriver 124F both Hammond
using different brands of 6SN7 tubes in different positions come from my sensibility and experience
6SNTWGT Sylvania recommended for heather cathode insulations
OTP its 1650T 1K9
ok thanks i will try if the amp come back for service from the customer
but I'm afraid that this cap can degrade phase opposition
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Why stability is a concern? There is no global feedback.
I am not sure that loading increases transformer's linearity, unless there is a self-resonance in the audio band that needs damping.
I am not sure that loading increases transformer's linearity, unless there is a self-resonance in the audio band that needs damping.
An interesting approach, I'd be worried about DC condition's drifting as the valves age. Clever that you managed to use no transistors or silicon and to use direct coupling all the way through, but diodes and transistors have their place, a diode between grid and cathode of CF's for instance helps protect valves on power up. I see you've no cathode decoupling on the OP stage and are you running the heaters of the 6550's in series. What are the hum + N, frequency response & THD at full OP power? What are the OPT's: Hammond 1650 somethings? Not keen on the choc blocks.
Andy.
Andy.
@ power up only heather transformer 150W 2X 6V3 ,no HT. heaters of the 6550 6V3 phase inversed
no noise at all see TFT
i forget small neon lamp grid cathode i d'ont like diode but HT switch allow tubes heat up before
6550 cathode resistor 10 ohm no need caps
no noise at all see TFT
i forget small neon lamp grid cathode i d'ont like diode but HT switch allow tubes heat up before
6550 cathode resistor 10 ohm no need caps
Nice amplifier! It's nice to see that many glas bulbs on the chassis 🙂
Can you explain how this amplifier is DC coupled from A to Z? I see an interstage transformer at the input and there is one for driving the screen grids of the output stage. This is inductive coupled in my book, not DC coupled.
Fully DC coupled is possible, but IMO would take a very different approach.
Only the VAS is DC coupled so I am not really expecting issue's with drift. I have designed and build several DC coupled amplifiers and never had much issue's with voltage drifting with small tubes. If you take proper care in your design then it should be no issue at all.
thanks Lechuck yes very good sounding amp , but i never said not writhe DC coupled, but DIRECT COUPLED no interstage caps
i do not try to pretend nothing just replay old professional hight power AB2 power amplifiers for home appliance
thats all. (power tetrodes also DC direct coupleds not only VAS)
the connections between the tubes are made in direct coupling and/or by inter-stage transformer.
i do not ask help no any idea for modifications, its well working from many months in my friend customer home studio
he having experience with very hig value amplifiers and feerless of HT tubes transmitting triodes and so on
have good journey cheers
claudiomas
i do not try to pretend nothing just replay old professional hight power AB2 power amplifiers for home appliance
thats all. (power tetrodes also DC direct coupleds not only VAS)
the connections between the tubes are made in direct coupling and/or by inter-stage transformer.
i do not ask help no any idea for modifications, its well working from many months in my friend customer home studio
he having experience with very hig value amplifiers and feerless of HT tubes transmitting triodes and so on
have good journey cheers
claudiomas
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Both the input stage and the output stage are inductive coupled. The energy litteraly has to go through the air, how is this direct coupled? No offence, but direct coupled in my book means that they are truly directly coupled without a L or C in between them 😉
yes i writhe this first post
all the connections between the tubes are made in direct coupling and/or by inter-stage transformer
to resume the input transformer 1:0.5/0.5 splitter dephasing
E80CC-6SN7GT-6SN7WGT direct coupleds
predriver transformer 0.5/0.5:0.5/0.5
6SNTGT direct coupled to 4X 6550C
take easy i'm not pretending to invent hot wather
just i like amplifiers like this
low value grids resistors and no caps
even and uneven harmonics equilibre sound like very dynamic big triode SE
wen williamson and Co means lot of odd uneven harmonics
all the connections between the tubes are made in direct coupling and/or by inter-stage transformer
to resume the input transformer 1:0.5/0.5 splitter dephasing
E80CC-6SN7GT-6SN7WGT direct coupleds
predriver transformer 0.5/0.5:0.5/0.5
6SNTGT direct coupled to 4X 6550C
take easy i'm not pretending to invent hot wather
just i like amplifiers like this
low value grids resistors and no caps
even and uneven harmonics equilibre sound like very dynamic big triode SE
wen williamson and Co means lot of odd uneven harmonics