Your journey with lower-watt tube amps -- Can a kit be good enough?

Hi @invalid ,

Yes most of vintage amplifiers use chokes in power supply.

But they use very small capacitors in B+.

The issue with small capacitors is not the 120Hz noise from AC , but voltage stability during playing of load and complex music.

I had DIY 300B amp that I tweaked and in the end rebuild it from scratch. For 300B is very important the driver tube (more powerful is better) and driver inter-stage transformer works much better compared to RC coupling. 

How many maximal dB do we need for classical, rock, jazz music?

It looks like the distortions from 50Watt heat on the speaker's voice coil and crossover parts should be much more horrible then 10% SET distortion on maximal power distortions. 

I built and now use my DIY amplifier not to save money but because I wanted to make an amplifier better than the market offers. 

I use output and interstage Hashimoto transformers plus James Audio and Hashimoto power transformers and Hashimoto chokes,

and many other expensive parts. Only the parts for my amplifier cost me $7000. 

My speakers are Alteс 604E. According to the passport, their sensitivity is 102 dB per 1 watt/1 m. In fact, their real sensitivity is 97-98 dB 1w/1m. 

The vast majority of manufacturers overstate the sensitivity of speakers. These speakers do not have very deep bass.It is around 40Hz.

So it makes the life of the amplifier easie.

My listening room is L-shaped, with a 300 square foot main area, a smaller 120 square foot section, and 8-foot ceilings.

I don't have any issue with playing super load +105dB and I don't have any issue with speed and bass in different styles of music.

But it took me many years to improve the amplifier and to make it sound good with different kinds of music that people think don't suit SET amplifiers.

Hi @mclinnguy ,

I never had Tamura output transformers. But I had James Audio.

Hashimoto gives more low level details then James Audio. It terms of tonal balance they sound similar.

But other tweaks that I did (cathodes, power supply capacitors, adding inter-stage transformer, changing driver tubes ) gave more difference than a simple change of output transformer.  

 Sun Valley 845 doesn't use an inter-stage transformer between driver and 845 tube.

845 is impossible to drive without IT! You get more driver tube distortions than 845 output stage distortions. You also can't get a good deep and fast bass.

The same I can say about 300B. But 845 is much more difficult to drive than 300B!

For PX25, 2a3, 45 output tube or if kt88/kt66/el34/6L6/6v6 used as SE output in triode mode you can receive a good sound without an inter-stage transformer.

Hi @hilde45 

The problem of 300B they need a driver with 150 volt peak to peak voltage swing. For 845 you need much more voltage swing.  

It is possible to drive 845 with RC coupling, but you get much more distortions vs IT drivers with the same tubes. With IT - the output tube can be driven when it is in class A2 and you get more power and better clipping recovery.

I have a DIY 300B amplifier and I used 6f6 in triode with RC coupling, then I changed to IT coupling. It was a huge difference! It sounded like a different amplifier. And I used super expensive V-Cap CuTF capacitors in RC coupling.

Then I changed the driver tube from 6f6 to 6v6 and to 5881 (6L6) and each time a more powerful driver sounded better, bigger soundstage with better instrument separation. 

Hi @atmasphere 

Thank you for your advice. I can try it if I build a new amplifier.

So. Do you think the issue is not voltage swing of driver but the current and power it should drive on capacitive load. And the power is function of the voltage swing in squire.

I had Spendor 2/3 speakers for around 5 year. A number of years I used the Plinius 8200 integrated to drive these speakers. But I felt something was wrong and I started looking for a good matched amplifier. I stopped on the McIntosh MC30 vintage monoblocks. It was a great match between amplifier and speakers. MC30 was better than Plinius in everything: more natural tone, better separation, better bass control, more musical. Then I bought an Altec 604E (102dB sensitivity by spec and around 98dB in real). Spendor 2/3 are 88dB sensitivity.

I used Altec with McIntosh first and then tried a 300B SET amplifier. The 300B DIY SET had a big advantage over the push-pull MacIntosh with highly sensitive Altec. Sound was so much more transparent, natural, musical and detailed. McIntosh had more powerful bass but SET bass sounded more natural. My current DIY SET is in a different league compared to my first DIY 300B SET.

One friend of mine moved from his modified Quad II to 300B SET. He builds DIY speakers. But he mostly used the big 15" JBL 4 way clone DIY speakers. These speakers are more difficult to drive than my Altec 604. And he also clearly prefer 300B SET over Quad II.

So, a good SET with matching high sensitive speakers will be a huge step over any vintage push-pull amplifier including Dynaco.

Hi @atmasphere ,

In parallel to the McIntosh MC30 I had Marantz 8b.

I used these amplifiers with Spendor 2/3 and Altec 604E with original n1500 crossovers.

This Marantz was burned by one of the previous owners.

So output transformers were fixed, and power transformer and choke was replaced by a local transformer store built. On another hand, I and one of my technician friends replaced resistors to RikenOhm, capacitors to Black Gate and signal capacitors to Audio Note tin and copper foil. The technician adjusted the feedback of the Marantz. So this Marantz 8B had pluses and minus versus the original Marantz 8B. I also used the original Mullard EL34 on this Marantz.

Yes this Marantz 8B sounded more clear then McIntosh MC30. But despite Marantz bass wasn’t bad, MC30 bass was on the other league. It was also a big difference in complex music reproduction. 8B was good on very simple music but the sound became muddy and congested with bigger number of instruments and voices. On the other hand, the complex music wasn’t an issue for MC30. The Plinius 8200 Mk1 integrated that I had then also had a problem with playing complex music, but it did it a little bit better than Marantz.

Hi @atmasphere ,

 Power supplies of all vintage tube amplifiers from 50-60x look so miserable with such small capacitors.  It is especially true for stereo amplifiers when PS is used for both channels in parallel without any separation. I can say for sure such a PS will not work for a SET amplifier without feedback even if it is just 2 watt power.   

How does it work in all these vintage amplifiers? Does feedback make them less sensitive to PS or the reason is the push-pull topology?