What tubes are used?

[Junm]

Hi does somebody recognizes this monoblock PP amp? Don’t know the tubes that were used. Somebody might help me out with the schematics. With 8k 10w output and directly heated tubes with input trafo.

 

[petertub]

My crystal ball has crashed, thus i cannot tell what amp it is. A picture might be advantageous ...

 

[Junm]

Sorry just had trouble uploading photos

 

[TheGimp]

Start tracing the circuit from the Sansui output transformer back. Post the schematic.

Search for the Sansui output transformer number. If you find it used in another amp, or find data on it it will help identify possible tubes.

There is a lot of information to be gained from the bottom of the OPT. Does it specify two tube connections and one B+? If so, it is 8Kp-p for push pull operation.

4 Pin output tubes, 5V and 6.3V filament supplies, not 2A3.

 

[Junm]

I dont have the actual unit yet so i just looking at the sent photos. As I see it has pp output with 2 4 pin tubes and 5 pins predrivers plus a 4 pin tube rectifier with 5 v filament.

 

[Eli Duttman]

The power trafo suggests the 125 mA. capable, 5Y3 equivalent, #80 as the rectifier.

The unit is obviously DIY and the schematic will have to be worked out by tracing.

Sansui used Hashimoto "iron".

BTW, that power trafo strikes me as being puny. Where is the filament current for DHT "finals"?

The #27 IDHT is possible in the small signal positions. However, the power trafo can't provide enough 6.3 VAC current for a pair.

 

[Wavebourn]

Japanese DIY amp?
I would ask this guy: Kanbo Yoshiba | Facebook

 

[HollowState]

The amp is definitely push pull and I would guess 6B4G or 6A3 for the outputs. Both are very similar. For the rectifier either an 80, 5Z3, 274A, perhaps even an 83 although unlikely.

 

[TonyTecson]

i saw that being peddled locally, is that a single block Jun?

 

[jazbo8]

Sansei used Hashimoto "iron".

I thought Hashimoto was started by ex-Sansui employees...

 

[TonyTecson]

after sansui closed down, the ex-employees started/continued with hashimoto....

 

[jazbo8]

Aso, from the Hashimoto catalog, I’m guessing the output tubes are 71A’s.
https://frank.pocnet.net/sheets/021/7/71A.pdf

 

[Junm]

Thanks for your input guys. Once i have the unit i will change output tubes and driver tubes maybe 6v6 or 6bq5. But im not sure if the power trafo will not be overloaded. Or triode outputs but 8k is to high for triodes. I might remove the input trafo and change it with 6sl7.

 

[jazbo8]

With all that changes, what’s the point of buying it in the first place?

 

[Junm]

i saw that being peddled locally, is that a single block Jun?

Yes a friend requested it to be restored or be upgraded to other affordable tubes. I will do conversion of tubes and maybe fit in another tubes as well as new circuitry.

 

[kodabmx]

It'll be easiest to use octals or magnoval tubes since the sockets will fit in those holes.
A pair of 6N8S/6SN7 for VA/PI and driver, and 6P3S/6L6 output perhaps?

 

[Junm]

With all that changes, what’s the point of buying it in the first place?

I didn’t buy this but my friend bought this s he want to have quality trafos even though its a monoblock. I’ma tube builder and those trafos and sockets worth less then a hundred bucks.

It'll be easiest to use octals or magnoval tubes since the sockets will fit in those holes.
A pair of 6N8S/6SN7 for VA/PI and driver, and 6P3S/6L6 output perhaps?

Yes koda, lot of option to go with but the buyer still have the interest as it is but maybe budget will caught her.

Japanese DIY amp?
I would ask this guy: Kanbo Yoshiba | Facebook

Ahh good point he’s my fb friend.

The amp is definitely push pull and I would guess 6B4G or 6A3 for the outputs. Both are very similar. For the rectifier either an 80, 5Z3, 274A, perhaps even an 83 although unlikely.

Thanks thats a good point to look with. But 8k pp trafo, are they suited for the opt?

 

[Alan4411]

With a small mains transformer (it says 80mA on it for B+) and an output transformer marked 10 watts at 8K ohms, stick to the 6V6 / 6BQ5 plan.

 

[jazbo8]

Changing the design, especially the output tubes seems like a fools errand... DHT to IDHP, really? Just trace out the circuit and get the correct tubes, even if they cost a bit more - you only need but a few of them for the monoblock.

 

[Junm]

With a small mains transformer (it says 80mA on it for B+) and an output transformer marked 10 watts at 8K ohms, stick to the 6V6 / 6BQ5 plan.

Yes if the owner wants an alternative. Thanks

Changing the design, especially the output tubes seems like a fools errand... DHT to IDHP, really? Just trace out the circuit and get the correct tubes, even if they cost a bit more - you only need but a few of them for the monoblock.

Thanks, You have a point that’s why i’m asking if someone is familiar with this. I can reverse engr this thing but im not so familiar with those dh tubes. And i wish they are still available at a reasonable price.