DIY Audio Projects Forum

New Tube Amp Ideas
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Author:  BowToEd [ 13 Jul 2019, 16:37 ]
Post subject:  New Tube Amp Ideas

I'm looking to make a new tube amp. This will replace the small amp currently in my living room.

I want a tube phono preamp stage, maybe with 12AX7 or 6DJ8. I'll also want a line level preamp to drive the power amplifier grids. I'm thinking 12AT7 or something.

Where I've got problems is making the power stage. I can do one of two things - I envisioned a pair of single ended stages using 12AV5GA or another horizontal deflection tube. This would be nice except the cost of transformers capable of a decent power bandwidth. Negative feedback can extend the transformer range, as well as using oversized iron. EG, getting 15w cores and running at 5w.

The other option would be using an IC power amplifier such as TDA2030 or so. I'm really only looking for 5-6w to drive some antique speakers.

If I went with a tube output, I would likely have a 300v power rail derived from one of those ZVS modules, and use the 12v rail for tube heaters and relay switching. I want relays to select the inputs.

If I go the route of solid state output, 12v in will be changed to around 30v for all analog electonics. The tube voltage won't be as high but no longer needing feedback around an output transformer will make this less of a problem.


Author:  Gab [ 15 Jul 2019, 07:28 ]
Post subject:  Re: New Tube Amp Ideas

As far as i know, output transformers with what I consider good bandwidth are always expensive, especially when looking for single ended ones. It depends on what you consider good bandwidth, and the speakers that are to be used with the amp. If your speakers don’t go below 60hz then smaller opt might be ok for you. Size and weight are always a good indicator of the sound quality of an opt, so the more you pay, the better the transformer will be. There are better transformers than others for a given size, but in general, the bigger ones will give a better low end.

My general opinion is that you should build your line level, phono stage and power amp as independent components. Frist, it would give you the opportunity to chose exactly what kind of circuit you will use for each one without being limited to what fit the other stages. Solid state phono stages are a lot simpler and can be powered with batteries, wich makes for a silent and simple to build stage. A lot less expansive too. By going the separate route, you also get the advantage of having a power supply for each component, wich is simpler than building a complex psu that has to power many different things. A preamp psu have different noise requirements than a power amp one. Finally it is also easier to fit each component into its own enclosure and to find troubles if there happen to be.

Author:  M. Gregg [ 15 Jul 2019, 08:01 ]
Post subject:  Re: New Tube Amp Ideas


So much to choose from, SE, PSE, PP,PPP, SET, SEP.

PP Transformers are normally smaller less weight in the iron circuit so less shipping cost.
However after using PP for years I only use SE now. Its strange to think years ago that SE was the top of the hit chart.
But now its all about PP is better. (what's the point?)

What to build is a very difficult question with PP the number of phase splitters is interesting.

Then there is power running cost which seems to be the "flavour of the month" at the moment.
Its interesting to see all the petrol sports cars in the second hand car lots with no one looking<<times change.
Lets not mention OTL :hot:

It all depends what power you want, what sound you want, what you want to run through it, because films and music are not the same animal.<<they should be shouldn't they if nothing is added or removed.

Here is a thought for you: (Don't bother with the 260G)<<<it gets a bit hot to many losses but I had it to use at the time.
Running EL84 SE.<<based on Dynavox and Marantz 8 input with Electron stream triode. Its just to give a couple of ideas.
Ie check the output Tx prices. If you want louder then its PSE or PP. Or go to medium power tubes it depends on how loud you think loud is. Remember that small tubes are used in guitar amps.

Have a look at the Manley stingray for inspiration (I have no connection its just for interest):

M. Gregg

Author:  Gab [ 15 Jul 2019, 09:13 ]
Post subject:  Re: New Tube Amp Ideas

Wow ! There is a lot going on in this chassis !!

BowToEd : you should have a look at the projects section on this website. is an other great project source, and claus biryth projects on the lundhal transformer’s website

Author:  M. Gregg [ 15 Jul 2019, 09:14 ]
Post subject:  Re: New Tube Amp Ideas

Another thought for you,

Look up EAR859 Tim de Paravicini.
There is a PDF on line of the circuit but I won't link to it 8-)

M. Gregg

Author:  BowToEd [ 15 Jul 2019, 15:44 ]
Post subject:  Re: New Tube Amp Ideas

First, I found a link to the power supply module I want to use...

These aren't something I've used before in an audio amp, so I may end up needing to provide additional filtering.

As far as i know, output transformers with what I consider good bandwidth are always expensive, especially when looking for single ended ones...

True. What I'm looking at right now is buying less-expensive SE guitar transformers and extending their range on the following two principles. First, I'm planning to buy a 10w transformer and use it to commute 3-5 watts of audio power. Second, I'm intending to use negative feedback to even out the frequency response in the amplifier. It follows that the transformer will have a lower output at the extreme lows and highs. Running with less current in the primary and less power through the core will allow the transformer a little more bandwidth. Negative feedback should chop down the mid-range that has the most output, so the frequency response should be extended at the expense of lower output. My intent is to apply something like 20 dB of global feedback.

4.90 VRMS is 3 watts in a 8 ohm load, meaning an overall voltage gain of 16.4 is required when the line input is 0.3 VRMS. To apply 20 dB of feedback, we need 10 times that, so let's say 164. A 5K - 8 transformer will have a voltage gain of 0.04. So, between the power tube and preamp tube, the overall gain would have to be 4100. Perhaps I would need two pre-amplifier stages to get up to that number. Calculating the power stage gain seems like it would be the hardest, so an empirical test seems like it would be the best way.

So let's say my power tube has a voltage gain of 15. That is, 15 VRMS appear across the transformer primary for an input of 1 VRMS. I need a total gain of 273 between two tube preamplifier stages, the first of which having no cathode bypass capacitor because that's where the negative feedback will go. A pair of 12AT7 stages will be more than enough to do this, and 12AX7 stages would be overkill here. Strictly speaking, two stages of gain would be able to do it easily but it's beyond the limits of a single tube.

The solutions are to have a ridiculous amount of gain so I can restrict it with feedback, or just lower the amount of feedback that I want to apply. 10 dB would mean I only need 51.82 total voltage gain, and 1296 gain into the transformer. Using my previous assumption of Av = 15 for the power stage, the voltage amp now just needs to be 86.4. That's easily do-able by a pentode stage. The biggest issue is that using lower feedback means my frequency correction capabilities are reduced. That's kind of important, although it could be excessive if my chosen transformer is already close to the limits of the audio spectrum. To me, the trade-off is purchasing a $35 output transformer and using some tricks to increase its performance, or purchasing a $165 transformer and sticking a triode-strapped pentode to it.


Author:  ILoveHiFi [ 15 Jul 2019, 21:51 ]
Post subject:  Re: New Tube Amp Ideas

I have a sound luster from china, orignally very disipationg sound quality.
After fully custom scheamtic modded exteremely still disapointed about the sound quality.
I haven't tried Push pull but I belive this one is king in sound quality.

Author:  BowToEd [ 15 Jul 2019, 22:20 ]
Post subject:  Re: New Tube Amp Ideas

I saw some cheap Chinese transformers for sale on Amazon. I think I'm going to go with a pair of OT10SE transformers. They should be more than enough. That's the whole point.


Author:  ILoveHiFi [ 16 Jul 2019, 03:41 ]
Post subject:  Re: New Tube Amp Ideas

Have you looked at aliexpress thats typically the place to look when your #China #Cheap
If your cheap shipping expect to recive items in 3 months time max at least 1 month

Author:  gofar99 [ 19 Jul 2019, 13:40 ]
Post subject:  Re: New Tube Amp Ideas

Hi, I have used those modules. They are generally ok. I add a R-C-R-C filter after them with snubbers on the caps. The output of the module is not clean enough for me. A 1HY choke would not be a bad idea either. (everyone knows I really hate hum and noise). Be aware that the output has a link to the 12 V negative input so if you need a heater lift circuit it can be a problem. Back to the original post...The phono section can be done it lots of ways. Some SE variations using 6DJ8s are pretty nice and simple. I prefer SRPP designs though. For the line stage I would think a 12AU7 would be about right. You really don't want a huge amount of gain. The other half of the 12AU7 would make a nice P-P driver as well. For SE the line stage would probably be sufficient all by itself. A SE with 6V6, EL84 or possibly 6AQ5 would probably be suitable. P-P with any of them would be my choice though, Run in class A if you have enough iron in the trannies.

Good listening

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