Help identifying the output tubes please

Oscillate · « **on:** 17 Nov 2008, 02:13 am »

I have a very basic question about the tubes in my monoblock amps.
Which pair are the 'output' tubes? Is it the two RCA-50s or the two DA3s?

To help clarify, the stated topology of the monoblock push-pull amplifier is:

The driver D3A (tube A) is run in single ended with an interstage transformer to 50 tube (tube A)
The driver D3A (tube B) is run in single ended with an interstage transformer to 50 tube (tube B)
Then the two type 50 are then run into a Push Pull OPT to sum phase A and Phase B

Thank you in advance for your replies

topround · « **Reply #1 on:** 17 Nov 2008, 02:21 am »

Well it seems the RCA 50's are your output tubes , you have one rectifier and two driver tubes. Don't know what the Da3's are but they drive. What are the RCA 50's , maybe 2 ,3 watts?

Enjoy!

Oscillate · « **Reply #2 on:** 17 Nov 2008, 02:30 am »

"What are the RCA 50's , maybe 2 ,3 watts?"

...I honestly don't know. These push-pull monoblocks are reported to put out 38 watts each.

topround · « **Reply #3 on:** 17 Nov 2008, 02:43 am »

I figured if they are running single ended they must be low watts,you should know. what speakers are you going to use them with? That is important

They could be killer with one pair and just shit with another, they need to be matched.

Oh these are Promitheus amps. Good Luck!

JoshK · « **Reply #4 on:** 17 Nov 2008, 03:29 pm »

Type 50 tubes are very expensive rare tubes (pairs go for $250 or more on ebay). They sit between the 2a3 and the 300B as far as output power, 5-6 watts (really dissipation rated). They are reported to sound amazing and are really sought after amongst the SET crowd.

D3A's are fantastic high gain, high transconductance tubes typically made by Siemens or Telefunken (they embarass 12AX7s). They are one of the best high gain drivers available. I am using them as drivers in my SET amp (in progress).

If the monoblocks are putting out 38 watts then they are likely running in Class AB2. In pure class A, one 50 puts out 5-6 watts, so push pull class A would be limited to 10-12 watts (2 x 5-6watts).

Oscillate · « **Reply #5 on:** 18 Nov 2008, 12:43 am »

"Type 50 tubes are very expensive rare tubes (pairs go for $250 or more on ebay)"

I paid approximately $850 for the matched quad of NOS Cunningham made RCA-50s used in the two monoblocks amps.
Yes, the amps are designed and made by Nicholas (Promitheus Audio). They sound very smooth and musical (no noted hum).
My current speakers are 87db efficient and see mostly HT usage. The GR Research LS6s I will be building are approximately
90db efficient and will be used for music only. If the LS6s don't get loud enough for my tastes, then I will probably build a set
of horns ...or buy a McAlister Audio sweep tube amp.

Maybe this link will help someone save a couple $$$

JoshK · « **Reply #6 on:** 18 Nov 2008, 01:16 am »

Quote from: Oscillate on 18 Nov 2008, 12:43 am

"Type 50 tubes are very expensive rare tubes (pairs go for $250 or more on ebay)"

I paid approximately $850 for the matched quad of NOS Cunningham made RCA-50s used in the two monoblocks amps.

That is what I call expensive for output tubes. Maybe not absurd, justifiable probably, but still expensive. Can I ask where you got your quad?

Oscillate · « **Reply #7 on:** 18 Nov 2008, 03:12 am »

"Can I ask where you got your quad?"

I purchased the matched quad from Nicholas. The push-pull monoblocks are a one-off item.
At that time, the only other available RCA-50s for price comparison were from this from this private seller in Japan.
In the future I intend to buy some of those inexpensive reissued RCA-50s as backups from the link I posted previously.