VTA M125 transformer heater filament rating

I am building an octal board for my VTA M125 and plan on using Shuguang CV181-t tubes in those positions. They need .9 amps @ 6.3v for their heater filaments. If I add all my heater values: 4x KT120 @ 1.95 each = 7.6 amps, Mullard GZ33 @ 3 amps, 2x Shuguang cv181-t @ .9 amps = 1.8 amps. Total 12.4 amps. Is the too much for these transformers? If so should I substitute a Weber WZ68 copper in place of the Mullard?

30 Ounce wrote:I am building an octal board for my VTA M125 and plan on using Shuguang CV181-t tubes in those positions.  They need .9 amps @ 6.3v for their  heater filaments.  If I add all my heater values: 4x KT120 @ 1.95 each = 7.6 amps, Mullard GZ33 @ 3 amps, 2x Shuguang cv181-t @ .9 amps  = 1.8 amps.  Total 12.4 amps.  Is the too much for these transformers?  If so should I substitute a Weber WZ68 copper in place of the Mullard?

The two 6.3 volt AC lines are rated at 5 amps each so - 10 amps total for the two 6.3 volt lines

The Mullard GZ33 is on a separate 5 volt @ 4 amp AC line.

1. If you do use the octal board, I believe you are at 9.4 amps with the octal board (7.6 amps for the 4 X KT120 and 2.9 amps for 2 X 6SN7 type tubes) and you will be approaching the 10 amp "rating" of the two 6.3 volt AC lines.

2. If you use the noval board with two 12AU7 type driver tubes (2 X 12AU7 = .6 amps) and your total current rating for the two 6.3 volt AC lines will drop to 7.6 amps and the amp will run noticeably cooler.

Bob

30 Ounce wrote:I am building an octal board for my VTA M125 and plan on using Shuguang CV181-t tubes in those positions.

I would be interested to know if you can get CV181-T tubes in both of those sockets. The sockets on the octal driver board are 1.7" apart according to Roy. The datasheet that I have seen for the Shuguang CV181-T indicates that the tubes are 50mm, or 1.9685",  in diameter. If that is accurate, you should not be able to plug two CV181-T tubes into the octal driver board.

It will be close, I was wondering the same thing...[url=https://servimg.com/view/20162508/1]

It will be close, I was wondering the same thing...[url=https://servimg.com/view/20162508/1][

That is about as close as you can get them!

So, given those those voltages approaching the 10 ampere rating, of the 6.3 V lines, are octal boards for the M-125, a bad idea ?.

if you stick to more conventional tubes (KT88 1.5A, KT90 1.6A) then that totals 7.6A max for filaments using 6SN7 drivers
even using KT120 (1.9A) gives you a max of 8.8A

Fair enough, it's always good to know the do's and don'ts. I only run KT120s, with novals, I will be trying the octals this week. By the way those octal boards are of very high quality, the assembled boards look awesome,

They do look awesome. The blue board with blue resistors look cool! Miflex caps make them look like pontoon boats though.

What's the word on those MIFLEX caps ?, those are huuuuge. They look like air compressor filters. Impressive.
Do you have previous experience with those?, I'm intrigued

Don Sachs built my preamp with Miflex caps in them and I was so impressed I thought I’d try them in my octal tube build. I should have this put back together this weekend.

Got them back together. Thought I’d start with KT88’s and see how warm the transformer gets and try the KT120’s if they don’t get too hot.

Holy font,!!!!!!!! I understand now why you were so adamant about sitting those Chinese coke bottles on the driving seats, They look awesome !!!!!!! VTA 125 twin turbo

Those amps look really nice all put together.

Thanks! I have about 15 hours on them now and everything seems fine as far as transformer heat goes. It sounds wonderful. I would highly recommend this combo of Miflex caps and Shuguang CV181-t if anyone is so inclined. It sounds so good I don’t want to put the KT120’s in!

Here’s a picture after several hours of use...beautiful!

30 Ounce I was waiting for your input before going that route..I see the cv181 closeness not much of an issue, they really look imposing. Have fun !!!!!

buchela wrote:What's the word on those MIFLEX caps ?, those are huuuuge. They look like air compressor filters. Impressive.
Do you have previous experience with those?, I'm intrigued

Miflex is a polish capacitor manufacturer (http://www.miflex.com.pl/en/products/audio-capacitors-and-filters). These caps are KPCU-01 - with thick copper foil and are quite heavy. I have them in my Lampizator Golden Atlantic TRP. According to some people they are as good as Duelunds, except they are much cheaper and have no oil inside. Sonically, they are very musical, a bit on the warm side but don't emphasize any frequency. Check out http://www.humblehomemadehifi.com/Cap.html for a review of various audio caps.

Thanks andyo,the link was very helpful, I'm ordering those

I would save those CV’s for the voltage amplifier stage only. From my understanding the phase splitter is less affected by the tube. They do like very nice though and you can do whatever makes you happy.

Update;  decided to give my KT120’s a try and use Weber WZ68 to ease the transformer stress and wow!  The dynamics and impact from drums and percussion is amazingly real on these amps.  I don’t know if it’s from the Weber WZ68 having more current available or because the Kt120’s are stronger tubes or maybe the Shuguangs can swing more voltage on the input...anyhow it is fun.  Horns are immediate and stunning,  acoustic guitar picking is very lively...

Any preamp ?

Yup, Don Sachs