Could be Oscillation with D3a tube and not oscillation with 6e6p tube in the same tube amp.!
The amp is D3a 45 300B tubes.
I think the amp with D3a triode mode ( u =77) sometimes oscillate.
With 6e6p tube with less amplification factor ( u =35 ) i think NEVER oscillate.
Too much amplification voltage could be the cause of the oscillation?
Thanks a lot.
santitrucco
The amp is D3a 45 300B tubes.
I think the amp with D3a triode mode ( u =77) sometimes oscillate.
With 6e6p tube with less amplification factor ( u =35 ) i think NEVER oscillate.
Too much amplification voltage could be the cause of the oscillation?
Thanks a lot.
santitrucco
If the 1K grid stopper is connected like in your earlier schematic (see link) than maybe that makes it more prone to oscillations. The grid stopper should be positioned between the control grid and the 100K resistor to ground (or, if there is a volume pot at the input, between the control grid and the wiper of the volume pot). The grid stopper should be soldered to the tube socket as close as possible.
https://www.diyaudio.com/community/...ram-it-is-a-single-ended-6e6p-46-300b.359409/
https://www.diyaudio.com/community/...ram-it-is-a-single-ended-6e6p-46-300b.359409/
stoppers are just at the end of the problem. what is the cause? D3a like high gm tube, is searching some care and precaution about the layout , it is not just plug and play.. of course need a separate capacitor and proper all Ub+ line decoupling. good guidline is that every tube must have separate each own capacitor. etc etc.
there is also oscillation through the heater line.. heaters must have also LC decoupling to the pins and to the gnd, L's must be mounted with 90 degrees between them..
there is also oscillation through the heater line.. heaters must have also LC decoupling to the pins and to the gnd, L's must be mounted with 90 degrees between them..
"Stoppers are just at the end of the problem."
Maybe it's a language thing but grid stoppers are meant to prevent the tube from oscillating. I agree that lay-out and proper decoupling of the B+ are also important but I really don't see why lay-out and proper decoupling would be more important than using a grid stopper.
As for the oscillations through the heater line. As far as I know LC decoupling of the heater line at (almost) every tube socket is something you see in equipment operating at high frequencies as to minimise leaking of these high frequencies through the heater line from one tube to an other. But in audio amplifiers this seems over the top to me because the tubes in audio amplifiers are not operating at RF/VHF/UHF. As far as I know this kind of leaking is not a problem at AF (I can't remember ever seeing an audio amplifier with LC decoupling in the heater line). And when one tube is oscillating like in the amplifier of TS, than stopping/preventing that tube from oscillating seems better to me than to prevent those oscillations from reaching other tubes.
Maybe it's a language thing but grid stoppers are meant to prevent the tube from oscillating. I agree that lay-out and proper decoupling of the B+ are also important but I really don't see why lay-out and proper decoupling would be more important than using a grid stopper.
As for the oscillations through the heater line. As far as I know LC decoupling of the heater line at (almost) every tube socket is something you see in equipment operating at high frequencies as to minimise leaking of these high frequencies through the heater line from one tube to an other. But in audio amplifiers this seems over the top to me because the tubes in audio amplifiers are not operating at RF/VHF/UHF. As far as I know this kind of leaking is not a problem at AF (I can't remember ever seeing an audio amplifier with LC decoupling in the heater line). And when one tube is oscillating like in the amplifier of TS, than stopping/preventing that tube from oscillating seems better to me than to prevent those oscillations from reaching other tubes.
Of course stopper is important, but is not only one thing like most people usually think. With bad layout, bad grounding, and high transconductance tube, stopper can't help you, i just wanted to highlight this..
RF practice like seen today is almost obsolete, it is good to mention from time to time how are the pins RF tube pins shunted with 1nF to center gnd lug.
High transconductance tubes like D3a and 6C45 can oscillate through the heater of course, and like reward gives not so amusing sound (artifacts from oscillation at higher f can be present in their lower band, close or in audio spectrum).
Im speaking about use high trans tubes in good designed widebroad audio amplifiers with 100kHz at least of BW, not "toys" of 10kHz or 25kHz where signal is dropping already from 3,4 kHz to up. I dont follow discussion when people are starting about bats and that, lost of humar hearing with time etc. Hi-Fi means hi fi, 0dB loss from 20 -20kHz is the target, not -3dB , and lets keep all the problems far away from audio band, how one my dear friend RF expert , passed away long time, liked to say, if the amp works well on 1MHz, then 20 kHz will be peanuts 🙂
RF practice like seen today is almost obsolete, it is good to mention from time to time how are the pins RF tube pins shunted with 1nF to center gnd lug.
High transconductance tubes like D3a and 6C45 can oscillate through the heater of course, and like reward gives not so amusing sound (artifacts from oscillation at higher f can be present in their lower band, close or in audio spectrum).
Im speaking about use high trans tubes in good designed widebroad audio amplifiers with 100kHz at least of BW, not "toys" of 10kHz or 25kHz where signal is dropping already from 3,4 kHz to up. I dont follow discussion when people are starting about bats and that, lost of humar hearing with time etc. Hi-Fi means hi fi, 0dB loss from 20 -20kHz is the target, not -3dB , and lets keep all the problems far away from audio band, how one my dear friend RF expert , passed away long time, liked to say, if the amp works well on 1MHz, then 20 kHz will be peanuts 🙂
For Audio ?
There is some Single End Triode amplifiers , with freq response -3dB 40hz 21khz , that sound a lot lot better than SS amplifiers without THD ,and infinity bandwidth.
I have been looking for RF build guidelines to no avail, can someone point me / us in the right direction?
Don't have to learn the theory to keep some rules.
This samples shows the "traditional" B+ powered equipment structure.... in my practice.
1.) Each stage has individual -local PSU- power supply /with two -possible twisted- wires/, "positive" wire decoupled from "main PSU" with (C) R-C/L-C stages (where C negative tied to local "negative" wire);
2.) Each stage has own local grounding point, where tied the "local PSU" negative wire;
3.) Local grounding points tied together as star ground (see picture) or strings to ground bus;
4.) Each channel has own grounding scheme; The channels grounding tied together -possible- on "main PSU" negative pole;
5.) To this local grounding points connected EACH component -which "grounded" within the stage-, so "local PSU" power smoothing capacitor/s/ "ground" too;
6.) Never share high gain tube's filament with other tubes!
7.) If you don't use filament elevating (to about quarter of tube's anode voltage), AC blocking of EACH filament pin is necessary (some nF to local ground);
8.) For high gain tube need to use grid stopper (100...10k), sometimes anode stopper too (10..few hundred Ohm carbon comp resistor);
9.) Never place too close high gain tube to another tube, or transformers/chokes; Sometimes tube shielding is necessary (mostly in phono stage);
10.) And so on.... 😛pp
This samples shows the "traditional" B+ powered equipment structure.... in my practice.
1.) Each stage has individual -local PSU- power supply /with two -possible twisted- wires/, "positive" wire decoupled from "main PSU" with (C) R-C/L-C stages (where C negative tied to local "negative" wire);
2.) Each stage has own local grounding point, where tied the "local PSU" negative wire;
3.) Local grounding points tied together as star ground (see picture) or strings to ground bus;
4.) Each channel has own grounding scheme; The channels grounding tied together -possible- on "main PSU" negative pole;
5.) To this local grounding points connected EACH component -which "grounded" within the stage-, so "local PSU" power smoothing capacitor/s/ "ground" too;
6.) Never share high gain tube's filament with other tubes!
7.) If you don't use filament elevating (to about quarter of tube's anode voltage), AC blocking of EACH filament pin is necessary (some nF to local ground);
8.) For high gain tube need to use grid stopper (100...10k), sometimes anode stopper too (10..few hundred Ohm carbon comp resistor);
9.) Never place too close high gain tube to another tube, or transformers/chokes; Sometimes tube shielding is necessary (mostly in phono stage);
10.) And so on.... 😛pp
There are people who can buy those -3dB 12hz 100khz amplifiers and would never buy them.
They prefer 10 watts from a SET, with -3dB 35hz 25khz..
Are they all fools ?
Will they be deaf ?
Haven't been able to listen to those broadband amplifiers ?
i am listening right now to a d3a headphone amp. (i actually built it with switches so i can chuck in 6e6p-dr). Oscillation was a problem until i put ferrite beads on the anodes (in addtion to grid stoppers as close to the pins as possible).
It was hard to pin down... as the d3as seem susceptible to interference (more so than 636p).
Its sounds great though now, and scoped shows no oscillation.
It was hard to pin down... as the d3as seem susceptible to interference (more so than 636p).
Its sounds great though now, and scoped shows no oscillation.