Ryan & Erwin's SSS #002 Madness

[Richard1001]

Using a 230 tap on 240 volt means all voltages go up. Not only the highvoltage. But the real risk is burning out the primary coil over time.

[Bombacaototal]

When quoting numbers like this you should specify which current measurement the % Pa max is based on (cathode or plate),

I completely missed this, sorry Martin. In my case I use the plate value as reference, although I know the correct is plate minus cathode. And I use this calculator to get the range

https://robrobinette.com/Tube_Bias_Calculator.htm

[Bombacaototal]

Using a 230 tap on 240 volt means all voltages go up. Not only the highvoltage. But the real risk is burning out the primary coil over time.

Thanks Richard, this was actually suggested by the manufacturer, and he mentioned the PT will be able to cope, but based on the experience so far I have been dubious and feeling less confident about their advices?

What you could consider now is using the 230V tap instead of the 240V, That will give you an extra 15 Volts of high voltage.

Our powertransformer can easily cope with the extra stress of 240V on the 230V tap.

I guess, if my PT was actually getting the correct 435V all the voltages would be higher as well. So if I follow the 240 into the 230, I just need to bring the dropping resistors back to original value.

If you were in my situation, would you scrap the second transformer or the marginal difference of 420V Vs 435V is negligible in the big scheme of things. I think I will experiment with the 240 into 230, rebias and see if I hear a lot of difference

[norburybrook]

Raphael, how does it sound at this moment? I'd play it and see...you might think it's the best thing ever.

Then start changing things.

M

[erwin_ve]

Using a 230 tap on 240 volt means all voltages go up. Not only the highvoltage. But the real risk is burning out the primary coil over time.

Thanks Richard, this was actually suggested by the manufacturer, and he mentioned the PT will be able to cope, but based on the experience so far I have been dubious and feeling less confident about their advices?

What you could consider now is using the 230V tap instead of the 240V, That will give you an extra 15 Volts of high voltage.

Our powertransformer can easily cope with the extra stress of 240V on the 230V tap.

I guess, if my PT was actually getting the correct 435V all the voltages would be higher as well. So if I follow the 240 into the 230, I just need to bring the dropping resistors back to original value.

If you were in my situation, would you scrap the second transformer or the marginal difference of 420V Vs 435V is negligible in the big scheme of things. I think I will experiment with the 240 into 230, rebias and see if I hear a lot of difference

Hi Rafael,

Best is to measure the heater voltage, 10% higher is acceptable (6.9v).

[Bombacaototal]

Raphael, how does it sound at this moment? I'd play it and see...you might think it's the best thing ever.

Then start changing things.

M

Thanks for the advice Marcus. I think it is too early for this assessment, as my other amps I really burnt them in and spent a lot of time dialing in the sounds.

After doing a few of those SSS inspired amps my assessment so far is that they are all siblings, all sound somewhat the same, obviously playing them back to back really allows to hear the nuances and differences, but in general, it is somewhat the same ball park.

The new one (420V) sounds great, and I enjoy playing it a lot, and after burning it in for 4hours or so I couldn't stop playing it, but I feel it has a bit less punch and "balls" compared to mine which runs 455V.

Best is to measure the heater voltage, 10% higher is acceptable (6.9v).

Thanks for the advice Erwin, will surely check it

[Synchu]

I'd be careful with the heaters - better slightly lower than higher, especially full 10%, esp. with power tubes - this inevitably shortens their life.

On the transformers discussion - I used Edcors in mine and very happy with the choice - they definitely know their stuff - and with hi-fi-ish style amps such as SSS variants - they sound great to my ears.

Niki

[Bombacaototal]

I have added a fuse in the CT of the HV. The spec sheet of the transformer states 320V at 0.7A for each side. Should I go for a 750mA fuse?

[Richard1001]

Are you talking about the same transformer? If so, i don't understand this specsheet. If the transformer could deliver 700mA per side at 320V, you would not have your low B+ issue. Together with the filament winding and according to those specs, this would make it a 500 VA transformer. Since all the power has to go through the iron core, your transformer should be substantialy bigger than a standard 100W twin PT.

My classic tone PT is 450mA per side at 345V (high tap) and a little more current on the 320V tap. So this transformer would be somewhere around 370 VA, and i had to use the 240V primary tap on 230V mains to get a B+ of 430V using the 320 taps.

Since both sides use the CT, I used an internal 1.2AT fuse on the CT. I have an external 1,6AT mains fuse. In case of a shorted tube, i want the external mains fuse to go first. The internal fuse is more or less a foolproof for the situation where someone would put in a higher value mains fuse after a short.

[Bombacaototal]

Are you talking about the same transformer? If so, i don't understand this specsheet. If the transformer could deliver 700mA per side at 320V, you would not have your low B+ issue. Together with the filament winding and according to those specs, this would make it a 500 VA transformer. Since all the power has to go through the iron core, your transformer should be substantialy bigger than a standard 100W twin PT.

My classic tone PT is 450mA per side at 345V (high tap) and a little more current on the 320V tap. So this transformer would be somewhere around 370 VA, and i had to use the 240V primary tap on 230V mains to get a B+ of 430V using the 320 taps.

Since both sides use the CT, I used an internal 1.2AT fuse on the CT. I have an external 1,6AT mains fuse. In case of a shorted tube, i want the external mains fuse to go first. The internal fuse is more or less a foolproof for the situation where someone would put in a higher value mains fuse after a short.

Hi Richard, thanks for the reply. Yes, it's the same transformer. I have attached the spec sheet for this conversation. Maybe he wrote the wrong spec?

I currently have a 2A mains fuse. For the CT of the high voltage the lowest value I had was 1.5A and that is what I have on that fuse now, but will buy some smaller value ones.

[martin manning]

Power transformers with center-tapped secondaries designed for two-phase rectifiers (where half of the DC current is supplied by each side) typically list the current capacity of the entire secondary. All current is returned through the CT, so a fuse placed there should be a bit more than the total HV secondary current specification. For example, a 450 mA Twin transformer (for a 100W amp) would require a fuse rated around 0.5A. A CT fuse is not the best idea for a transformer with a bias tap since the bias circuit provides an alternate ground return if the fuse opens. However, in the case of the (standard) SSS where the bias voltage is taken from the HT, this is not a problem as long as one end of the fuse is connected only to the CT lead.

[Bombacaototal]

Power transformers with center-tapped secondaries designed for two-phase rectifiers (where half of the DC current is supplied by each side) typically list the current capacity of the entire secondary. All current is returned through the CT, so a fuse placed there should be a bit more than the total HV secondary current specification. For example, a 450 mA Twin transformer (for a 100W amp) would require a fuse rated around 0.5A. A CT fuse is not the best idea for a transformer with a bias tap since the bias circuit provides an alternate ground return if the fuse opens. However, in the case of the (standard) SSS where the bias voltage is taken from the HT, this is not a problem as long as one end of the fuse is connected only to the CT lead.

Thanks Martin, makes sense, he is probably listing the total current. In my case then with the 700mA HV, a 750mA fuse should be enough? Indeed, the fuse is only connected to the CT and the other side to ground.

[Richard1001]

Power transformers with center-tapped secondaries designed for two-phase rectifiers (where half of the DC current is supplied by each side) typically list the current capacity of the entire secondary. All current is returned through the CT, so a fuse placed there should be a bit more than the total HV secondary current specification. For example, a 450 mA Twin transformer (for a 100W amp) would require a fuse rated around 0.5A. A CT fuse is not the best idea for a transformer with a bias tap since the bias circuit provides an alternate ground return if the fuse opens. However, in the case of the (standard) SSS where the bias voltage is taken from the HT, this is not a problem as long as one end of the fuse is connected only to the CT lead.

I don't think you are correct Martin. I can agree that the current would be for the whole coil (450ma / 690V ) but when the coil is split in two by a centertap, both coils can still provide 450mA , only the voltage will be devided in two. So instead of one 690V 450ma coil, you get two 345V 450mA coils. The total amount of power that can be delivered by the transformer stays the same.

[martin manning]

See under full wave capacitor input load: https://www.hammfg.com/electronics/tran ... eferer=968

[talbany]

Wall Voltage standard in the U.S after the war was rated 117V (small appliances) although, depending on where you lived universal coverage of this standard was not fully reached until around 1967 so most rural parts of the country ran as low as 115 well into the 50"s..Most of the older 60's Twins I've seen ran in the range of 438-448 @ 120V.AC ( I don't remember seeing any above 450V)..This would drive me crazy when these so called vintage transformer companies would advertise Vintage spec's then send you a transformer that was 460/470 for a Fender Twin or 59 Bassman (Including Mercury).IMO if you are shooting for an old Fender replica you generally want to try and keep the plates below 450V DC.
.. BTW. My 49 Tweed Pro with the original Triad P.T(Tube rectified) is dead on 447 @ 121VAC Pri.

Tony