6G4B SE Amp.

[redwine1118]

Hi there,

I am going to build one SE Class A amplifer with 6G4B and I would like to ask the comment from your goodself :

1) Do anyone have the schematic of 6G4B (in parallel) SE?
(My requirement , one stage amplification (6SN7, 6C45pi, WE417) RC couple to 6G4B)

2) In compare with 300B, 211, if I would like to bulid a power amp for a 15W class A output, will 6G4B got any tone difference with the above 2 tubes?

3) I understand that the output transformer is an important issue, will there be any recommendation?

My speakers : Roger LS3/5
Pre-amplifier : audionote M7

Red

[SHiFTY]

Use any 2A3 parallel single ended (PSE) schematic. The 6B4G is exactly the same, but with a 6.3V 1 amp filament.

One thing you might want to do is use DC filaments- these babies hum a bit otherwise.

And luckily the Sovtek 6B4Gs are pretty darn good (if a bit dark looking- the filaments are totally enclosed) They can be run at much higher plate dissipation too.

Here are a couple of ones I dragged up on google- don't know if they are any good tho.

http://digilander.libero.it/paeng/a_2a3_PSE_AMP.htm
http://www.audiodesignguide.com/my/pse3.html

I have to ask though- given the cost of paralleled 6B4s, why not just build a 300B amp for the same 7-8W?

[Brett]

Originally posted by redwine1118
1) Do anyone have the schematic of 6G4B (in parallel) SE?
(My requirement , one stage amplification (6SN7, 6C45pi, WE417) RC couple to 6G4B)

As Shifty points out, any paralle 2A3 amp will also work except for the heater. However 2 6B4G in // present a hefty load (>120pF) to the driver

2) In compare with 300B, 211, if I would like to bulid a power amp for a 15W class A output, will 6G4B got any tone difference with the above 2 tubes?

You're not going to get 15W reliably out of 2 6B4G in //. The sonics will potentially be vastly cifferent between 6B4G, 300B (hugely overrated tube) and 211's depending on what you build and how well. You can do 15W from a single 211.

3) I understand that the output transformer is an important issue, will there be any recommendation?

OPT is very important. For which tube? You have lots of choices and a recommendation would depend on your budget.

[Paul Barker]

I agree with Mr Grunty.

In general you have a good idea. The 6b4g is still available at sensible prices NOS. OTOH the mesh plate 2a3's sound very nice, if I were building an amp of that type those are what I would now go for money no object. If money were an object I'd use the Sovtek 2a3 in preference to the 6b4g because of the 2.5 volt filament, which is more easily AC heated.

Parallel Sovtek 2a3 output stage with just 2.5v filaments also presents less heater hum problems than a 5v 300b.

Then there is the matter of sound difference between 2a3, 300b and 211.

IMHO 2a3 is preferable all round to 300b. 211 has a beautiful silky smooth and delicate mid range and HF presentation, but due to constraints in output transformer design and power supply requirements a well executed 211 design is far more involved than a parallel 2a3 design.

For the parallel 2a3 idea you need to be thinking of three stages, a low impedance driver preceded by a voltage amplification stage. Actually it's all available inthe 6em7. Your 2 stage ideas are a compromise in terms of amplifier sensitivity. Of course if you don't need much sensitivity then that's different.

[redwine1118]

Dear All,

Thank you for your opinion.

Another question, if I connect EL34, 6550 or KT88 in triode mode SE, it will help me to save a lot of budget.

In compare with a 2A3 cct., will it be better?

Rgds,
Red

[Brett]

Originally posted by redwine1118
Another question, if I connect EL34, 6550 or KT88 in triode mode SE, it will help me to save a lot of budget.

In compare with a 2A3 cct., will it be better?

Define better for you. I know what it means for me, but not what it means for you. It will likely be cheaper, but not by that much, might have a bit more power, and based on my previous experiences, likely have more distortion with the EL34/KT88. A 2A3 will need about 50% more drive voltage, so might need some different driver choices.

It all depends on how you do it.

[Paul Barker]

You can get 12 watts SE from a 6550/kt88. Indirect heating so no hum problems. I've not tried it though.

[Happy Ears]

Hi , keep in mind the totaly different sound between directly and indirectly heated tubes ..
Altough a well designed 6550/KT88 amp ( triode connected ) can offer great sound , in therms of transparancy / depht etc. a DHT is far better .
Anyhow , Svetlana offer great 2A3/6B4 single plates for ridiculous price . go for it !

Happy Ears

[Paul Barker]

I love my dht's too, but the 6em7 power section has qualities no dht has, yet without having what they do have. There are differences, not necessarily superiorities. Secondly the 6a5g sounds for all the world to me exactly like a 6b4g. I haven't heard an R120.

That said I listen to a great really big dht at the moment out of preference, and I've decided it's finally time to build that PX4 amp.! I've now got old enough that my PX4's will outlive me, so I feel OK about using them.

[NickC]

Recently i built a se el34 been driven by a 5842 and it was triode connected with fixed bias been used in driver and output tube can be viewed at my sight . When i switch over to the 2a3 the sound became more musical and had more body. The 2a3 switch was a profound switch but i had the tubes on loan so it was allright in terms of cost. The 2a3 was a sovtek.