I would say:
1. Fewer stages and lower gain. Why go for 300b when maybe 45 tube or 801a might be fine?
2. Miles Prower puts it very well when he says "Good ISTs aren't cheap, and cheap ISTs aren't good. It's easily the priciest component you'll be using, and good ISTs can easily cost more than good OPTs".
3. So my suggestion is to think about your needs and budget first. I have heard a few amplifiers with IST's that were simply phenomenal. Every one of them was very expensive.
Ian
I am also living in Zürich, and meeting other tubeamp fans would be nice indeed 🙂
Dear all,
again, thanks for the valueable input.
I will start with my old OPT and I have in my mind to source either from Lundahl or Sowter the interstage transformers.
I don't need 7-8 watt to hear Music. I have a certain age already that I can enjoy music on low levels.
questions remain:
Dirk
again, thanks for the valueable input.
I will start with my old OPT and I have in my mind to source either from Lundahl or Sowter the interstage transformers.
I don't need 7-8 watt to hear Music. I have a certain age already that I can enjoy music on low levels.
questions remain:
- I can stick with low mu stages, also for a 2stage design. Is there any favorable triode as a driver which is still available for a reasonable cost?
(maybe any circuit available. I have seen the circuit from mbrennwa, which looks really interesting) - tube rectifier or solid state?
Dirk
I have few questions if you don't mind to answer.
- Can 6N6P tube be used as driver for this schematics same layout as in schematics?
- Negative voltage -74V, in website schematics is not shown, will you post it if possible?
- I can see on schematics that, no cathode resistor is connected to any output tube, will it be better to add a resistor? Or, should be used specific output transformer.
Appreciate your reply.
Hi Losi
With your 2.5k output transformer you can also use 2a3. You could also directly couple the circuit instead of using a transformer.. 😉
Transformer coupling means you need to buy a good quality interstage transformer. The Lundahl 1660 has primary inductance of 290 Henries, which is good. But you will still find that you need to use an input tube with really low Rp to use it like the two schematics posted so far... otherwise you will have low frequency roll off.
Ideally you need a triode with an Rp under 1k ohm to minimize the low frequency roll-off. The triode connected D3a has an Rp of 1.9k so it is not ideal.. the doubled up E88CC triodes have a combined Rp of 1.25k - somewhat better.... The russian 6n6p might be even better doubled up in the schematic of - check the specs sheets - I think it would have a combined Rp of 900 ohm, which might be very good.
Btw - some people actually LIKE low frequency roll off. Go figure...
Ian
With your 2.5k output transformer you can also use 2a3. You could also directly couple the circuit instead of using a transformer.. 😉
Transformer coupling means you need to buy a good quality interstage transformer. The Lundahl 1660 has primary inductance of 290 Henries, which is good. But you will still find that you need to use an input tube with really low Rp to use it like the two schematics posted so far... otherwise you will have low frequency roll off.
Ideally you need a triode with an Rp under 1k ohm to minimize the low frequency roll-off. The triode connected D3a has an Rp of 1.9k so it is not ideal.. the doubled up E88CC triodes have a combined Rp of 1.25k - somewhat better.... The russian 6n6p might be even better doubled up in the schematic of - check the specs sheets - I think it would have a combined Rp of 900 ohm, which might be very good.
Btw - some people actually LIKE low frequency roll off. Go figure...
Ian
I can provide some answers..
1. I think you could use 6n6p, but also be aware that it has an amplification factor of around 22 - which is less than ecc88 and much less than d3a. If you double up the triodes you would have a lower Rp and less low frequency roll-off.
2. Its just a negative bias power supply... This is quite easy to build. I suggest google or search the forum.
3. These are DC heaters, but I can't see why you could not use a 1 ohm resistor connecting the -ve to ground. This would make it easy to measure current flow while adjusting bias.
Ian
np. I think it was discussed in another thread a few years back. I reached that design after trying multiple other approaches, and just really like how it sounds.
We will disagree on this, what comes before the last cap has a huge impact on the sound of the amp, particularly an SE triode amp. Even the DDAC thread is full of discussion on choke input supplies improving a SS DAC 😉
If the design is implemented using a swinging choke it should have a minimum current through it, hence bleed resistor.
excellent 😀
You attached pretty strongly, so I defended robustly, nothing more. As for pride of ownership, I think you are reading to much into this. The design is almost 20 years old, I know it has worked for a bunch of people, and has been kicked around on here a few times in the past. I've heard better, I heard worse, I was just trying to answer the OP, an unusual response apparently 😕 😉
np. I also like gas regulators and mercury vapour rectifiers, they look cool, but I don't often use them in my amps.
all the best SJS
Dirk
Yes, it is easy to switch to triode D3a, or EC8010, or 6C45PI or 5842 😀
You would have more gain with D3a or EC8010, but don't forget you need to take great care to control VHF/UHF resonance, all these tubes like to work up there and will freely go off on one if you don't address it.
yes, diode in the cathode circuit would replace the resistor/capacitor pair
you have the Hammond, use it for the time being and confirm to yourself the amp is better than the last 5842-300B amp you built with the same OPT. I have just been asked to work on an amp using this OPT, and its seems ok, the biggest shortcoming of that amp is AC heating the 300Bs which just kills everything, and changing the OPT would not improve that!
I can't really recommend another OPT to try tbh, but if I were going to build this again I would probably go for Monolithic Magnetics S-9 and one of their ITs and use a Rod Coleman filament regulator. why? I like the way they approach the design, and the wide bandwidth they achieve.
You can go for cathode bias if you want, but I don't like it, I prefer fixed bias as I am looking for a fast, clean, punchy and dynamic sounding amp, hence the choke input supplies and fixed bias. I am not a lover of the warm soft cuddly glow of many SE 300B amps tbh.
best of luck
I think many of us would agree with this, the challenge is the "if well designed and built" 😉
The 300B is harder to drive then at first it appears, and a good strong driver stage can be really advantageous, but the whole discussion on how to build a great 3 stage 300B amp is a whole other thread.
The OP asked for a 2 stage amp with IT, which can sound really very good if well implemented.
best of luck
Thanks.
6N23P tube can replace ECC88 and sounds is better to my ears.
I was thinking to build this amp as I have part beside the IT. The question is, do I have to change anything in circuit if I use capacitor instead?
Appreciate any reply.
bekim
Just a note, I am one of the people who have built the SJS circuit and I thought it was great. Only change I needed to make was to put grid stop resistors on the 417a. When I built mine (ca. 1998) WE 417a's were pretty easy to find, but of course, not so much anymore. I used the SJS 1:1 IT and Power Transformers, but my OPT was a monster AN transformer designed for parallel 845's. I'd probably still be using this today but I burned up a winding on one of the PTs, and honestly, they were too much to lug up and down stairs when I moved to a 3 story house. My current 300B monos use Thoreston's design with an EL84 driving the 300B, and OPTs are now MQ.
this circuit was successfully built by a number of people, most frequently as a pair of mono block amps
You can replace the 417A / 437A with a triode D3a, EC8010, 6C45PI or triode E55L if you wish.
For 1:1 IT you could try the inexpensive Hammond 126B, or similar 1:1 offerings from SP Wound Components, Audio Note UK, Hashimoto, Monolithic Magnetics or Noguchi depending upon the depth of your pockets. I would suggest 1:1 bifilar wound are the way to go.
Nowadays I would definitely use Rod Coleman boards for the 5V filament supplies to the 300B! and be tempted to use SiC diode bias on the input tube
Best of luck
I'm kind of curious about the tube rectified bias supply.. Especially with an EZ81 which is indirectly heated.. There would be a delay as the rectifier warmed up before that supply would be up to voltage. You could potentially run into an issue where you have B+ on the power tubes, but bias supply isn't up to where it should be yet..
Why not use diodes for this?
The ez81 version of the supply sounded much better than the silicon diode version IMHO
The relay in the bias supply enables and disables the main ht to avoid the problem you raise.
If doing it today I would build it with separate mains tx and switch the primary of the ht tx with the bias supply relay.
Hello,
It would be so nice to see the schematic that SJS included in his post #8, now in the realm of IMAGE DEAD. Could anyone please post an attachment of that circuit? Or, mod, if no one could do that, could you please remove the temptation of this thread...i.e. just delete it?
Most frustrating to find a tempting thread that leads nowhere because of a dead image.
Can we not do better?
Robert Chambers, Corinth, Vermont USA
It would be so nice to see the schematic that SJS included in his post #8, now in the realm of IMAGE DEAD. Could anyone please post an attachment of that circuit? Or, mod, if no one could do that, could you please remove the temptation of this thread...i.e. just delete it?
Most frustrating to find a tempting thread that leads nowhere because of a dead image.
Can we not do better?
Robert Chambers, Corinth, Vermont USA
@PRR has provided a copy of the circuit, many thanks for that.
I built something similar earlier this year as a pair of 5842 - 2A3 mono blocks using Monolith Magnetics iron and Tentlabs filament supplies, it achieved 7.5 Hz to 90 kHz -1 dB at 1.0 Watt output.
For 300B I would probably use triode strapped D3a or E810F as discussed earlier in the thread if it has to be a two stage amp.
PRR, SJS,
Thank you for the schematic PRR, and for your comments SJS. My confidence is restored and I am back on track with this thread.
I am curious about the driver valve possibilities...5842, D3a triode, 6E5P triode and another I have just recently discovered, the WE 404A triode...need more study time on those options. I have Hammond 126C and also Tango NC-20 that I could try, just need to get going.
Very Best, Robert
Thank you for the schematic PRR, and for your comments SJS. My confidence is restored and I am back on track with this thread.
I am curious about the driver valve possibilities...5842, D3a triode, 6E5P triode and another I have just recently discovered, the WE 404A triode...need more study time on those options. I have Hammond 126C and also Tango NC-20 that I could try, just need to get going.
Very Best, Robert
SJS,
In your 317A/5842 driver version, do you use grid stoppers or ferrite beads...if so, please elaborate.
Robert
In your 317A/5842 driver version, do you use grid stoppers or ferrite beads...if so, please elaborate.
Robert
Audio Note Kits page 9, dif pinouts - 6sh7 (8pin octal)= 6au6 (7pin min)
https://www.ankaudiokits.com/ankmanuals/Interstage 300B Monoblock V 3.05.pdf
Parallel 300b page 9 again
https://www.ankaudiokits.com/ankmanuals/Interstage 300B Parallel Monoblock V 3.08.pdf
See post #28 (this is still sitting on the breadboard)
https://www.diyaudio.com/community/...rstage-transformer.323357/page-2#post-5819227
https://www.ankaudiokits.com/ankmanuals/Interstage 300B Monoblock V 3.05.pdf
Parallel 300b page 9 again
https://www.ankaudiokits.com/ankmanuals/Interstage 300B Parallel Monoblock V 3.08.pdf
See post #28 (this is still sitting on the breadboard)
https://www.diyaudio.com/community/...rstage-transformer.323357/page-2#post-5819227
Last edited: