Here's the circuit I used. The amps were monoblocks with an Angela Instruments Universal power transformer, 5U4GB and CLC power supply with RC filters after that for the input and driver tubes. I built that circuit back in 2007 and used it for several months before moving on to try a number of other input/driver circuits. This was always one of my favorites though.
6SL7/6BL7 driven Electra-Print 300B
- Thread starter maynard999
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- 300b 6bl7 6bx7 6sl7 electra-print
You’re right. It had more gain than I wanted, but it sounded good and that was my main concern. You can always out a pot or fixed attenuator on the input if the gain is a problem.
It goes without saying that there are tons of highly-successful tube amp products using PCBs, from Acrosound to Dynaco to a majority of modern products (ie; EFB, Audio Note). Of course many choose to build point to point, most likely in no small part because it avoids the equipment to produce a PCB. We all have our preferences and choices but it's a little silly to debate the success of one or the other.
maynard999
New Member
Yeah GL with your project.
This comment is music (no pun intended) to some peoples ears, but blasphemous to others...
In a no feedback amp, tube rolling will change the "sound" of the amp, most likely due to the changes imparted to distortion, gain, frequency response, etc. The tube itself does not have any mystical properties that make it sound better than another such as black plates vs gray plates or big getter vs small side getter.
Without test data (distortion, gain, frequency response, etc) or a means to measure it tube rolling is just a shot in the dark and romantic at best. Software based test equipment is very affordable nowadays and everyone has a computer. Some would rather spend exorbitant money on tubes rather than test equipment to help guide them on their journey.
Don't mind the haters... most are just solder slingers.
maynard999
New Member
To clarify, my earlier post was a joke. Not an attack on anyone.
I was seeking advice about a project and the thread was taken over by a discussion about my decision to use PCBs. My joke was pointing out that we all embrace PCB devices in one way or another. Most of us use DACs, and WIIM, other other streaming devices in the signal path. PCBs in audio is obviously not a sin. We obviosly use computers and cell phones too.
I have put in the time to learn PCB design. Others have put in the time to get good at point-to-point. There's good and and bad PCB design. If I made a beginner mistake where I ran a AC heater trace next to a signal wire or a thin high current trace, then yes please point that out. I don't think you'll see that in my designs.
BTW, I don't see anyone questioning Pete Millett or John Broskie about they're choice to skip point-to-point when they comes up with a new design. Why am I gettting it?
I was seeking advice about a project and the thread was taken over by a discussion about my decision to use PCBs. My joke was pointing out that we all embrace PCB devices in one way or another. Most of us use DACs, and WIIM, other other streaming devices in the signal path. PCBs in audio is obviously not a sin. We obviosly use computers and cell phones too.
I have put in the time to learn PCB design. Others have put in the time to get good at point-to-point. There's good and and bad PCB design. If I made a beginner mistake where I ran a AC heater trace next to a signal wire or a thin high current trace, then yes please point that out. I don't think you'll see that in my designs.
BTW, I don't see anyone questioning Pete Millett or John Broskie about they're choice to skip point-to-point when they comes up with a new design. Why am I gettting it?
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I think he was speaking to you, not about you.
maynard999
New Member
THD+N, post above edited. I misread what you wrote. Sorry for that.
I'm mostly just unwilling and unable to invest the time and money to buy and audition piles of tubes to try and find the magic combination. Some people enjoy it, but to me its just frustrating.
And these devices you listed are all low voltage with no high current AC anywhere near the signal path, with boards designed by engineers who have years of experience for products that are well sorted out and are mass produced. On this, you have designed PC boards for it, not sure if you have ever designed a PC board before and you have never heard this circuit play music.
I've dealt with several PC board tube amps that had hum and other issues related to bad PC board layout. Others that died an early death due to heat from the power tube or others parts being near the PC board. I'm just questioning why, as your first amp, you would add another place for it to fail that isn't easily repairable?
The other point: no one has even said "This tube amp has PC board construction!" as a bonus feature. For a one off amp with a simple circuit, there just isn't any advantage.
You asked for last minute feedback in the original post and when you stated you "are not skimping", seemed to imply that you believe going "Full PC board" gives some sort of audible advantage. Now if you had stated you were using silver wire etc, that would make sense. IMHO going "full PC board" is a downgrade. You stated in an earlier post each type has advantages. I'm just not seeing any advantage to using PC boards for a one off build like this at all.
For me it's the reason I use tube amps, to be able to tailor the sound by changing tubes until it fits my room/speakers, ears best. I've had instances where changing one tube would totally open up the sound stage and create the audio joy many of us are searching for. Yes it's a pain, takes a lot of time and buying enough different tubes to do this can be "expensive", but in a hobby where some folks spend $50K on speaker cables or $30K for a tone arm, tube rolling is pretty cheap
I know some folks don't believe things like the brand of capacitor should impact sound, a $1 coupling cap should sound identical to a $15 one and that all tubes should sound the same or something is broken. So should every tube amp sound the same no matter what types of tubes are used?
I don't want an amp like that, because then it can't be tuned to my taste. And I also believe (this is my opinion, not trying to state this as a fact), Iow and zero feedback tube amps just sound better to my ears. If I wanted the sound of a high feedback amp, I'd just use a solid state device. I'm constantly being surprised by how minor changes can impact the sound, like isolation pucks under the speakers etc. If there were no changes to be made to improve the sound, I wouldn't enjoy this hobby!
the problem with that for me is instead of getting satisfaction out of it, I get frustrated and end up not using it. It ceases being a source of enjoyment and relaxation and turns into one more puzzle to solve. I solve puzzles all day, and I need to be able to turn my brain off sometimes.
maynard999
New Member
The advantages for me are a compact and clean build that is modular. It's also an advantage because I'm extremely proficient with Eagle and can kick out a new design in no time, upload it to a PCB house, and have a FedEx at my door in days. The modular PCB approach works for me. I may try out a few other driver designs and it will literally be plug and play. Regarding my PCB designs themselves, the traces are oversized copper (copper is not a concern for me) and optimized to be as short as possible. There are no vias, ground planes where they make sense, etc. HV, LV, and signals are separeated, etc. The layouts are well thought out. I've been selling some of my designs on eBay for years and have 100% feedback. I have countless positive comments about the board layouts and designs. Regarding no skimping, I was speaking about components (Monolith transformers, etc).
You'll notice that my comments speak about preferences that work for my preference and abilities. Some share these preferences. It's OK if others have different preferences. Please do what works best for you when it comes to construction. I promise not to criticize the choices you've made that complement your skills and preferences.
You'll notice that my comments speak about preferences that work for my preference and abilities. Some share these preferences. It's OK if others have different preferences. Please do what works best for you when it comes to construction. I promise not to criticize the choices you've made that complement your skills and preferences.
Those are commercial products built to be sold. The PCB is simply the fastest and least expensive means by which to transport the technology to buyers. I don't buy them though, for the same reason I advise others not to build tube circuitry this way. Yes, G10 is long lasting and can be almost as sturdy as a metal plate. However, component positioning is fixed, and lead spacing is usually fixed, too. Even if the design is electrically perfect (and it sometimes is not), this construction method can present significant difficulties down the road when parts need to be changed. Just try to replace a small tubular polystyrene capacitor with a big, square Russian replacement. Or a resistor on pads originally designed for .012" leads with one having .040" leads. How you build is up to you, of course. These comments about PCBs and point-to-point shouldn't be taken as criticism. It's just intended as friendly advice in a forum that we all visit for the enjoyment of working with this older technology. Carry on and keep us posted on your progress!
Jack
trainbuffton
Active Member
The design looks solid enough that you could go ahead and order parts and build it. If theres something that needs tweaked along thec way, then youll handle that as it comes up. One reason that alot of us dont touch circuit boards is that we realize the limits of modeling software and we know from experience that tube circuits require some empirical tweaking before they're right. Point to point wiring is easer to modify neatly after the fact. Pcbs you get one shot before traces start sliding around and liting and then you scrap everything on the board and start again as if money grows on trees...
Plenty of good tube amplifiers have been built using circuit boards.
The very best of the best use tag board or point to point.
Plenty of good tube amplifiers have been built using circuit boards.
The very best of the best use tag board or point to point.
maynard999
New Member
Trainbuffton, appreciate the thumbs up. I was looking for some recommendations or a "go ahead" from a few experts. The power supply and filament supply are just slight revisions of boards I've built before. There's very little risk of anything going south with those. I see slight risk with the driver board. That's where the modular approach removes some risk. If I have to redo that board, I can cut a trace here and there or get a revised one on order. I won't have to replace or rework something the size of a motherboard.