Filament Transformer

[dejanm]

Hi,

I have read somewhere that having dedicated filament transformers (6,3 V, several A) for every channel is better though more expencive solution. Does somebody have experience with dedicated filament supply and does it really bring hearable advantages ? If yes - any transformer recommendation please ...

The alternative is of course transformer with several secondaries whereas two are 6,3 V secondaries.

Another question - if I use such transformer but for a mono blocks than I might be using only one 6,3 V secondary per box. For some transformers (and for some that is not the case) this may be a problem because of not balanced load on these 6,3 V secondaries. Does anybody know why this is the case ? Is it true at all ?

Thanks in advance
Dejan

 

[SY]

I don't think you need one for each channel, but separating the heater transformer from the high voltage transformer carries a major advantage- when the HV and heater windings are on the same core, rectification noise can couple from the HV to the heaters. It is not that difficult to filter out, but it is certainly better not to have it there in the first place if cost and size are not considerations.

 

[dejanm]

Do you have any recommendation for these transformers ?

 

[ArtG]

I recently completed a stand-alone filament supply that will eventually power two ST-35 amplifiers, preamp, and tube crossover. While it's going to be awhile before it's fully implemented, the benefits of doing this are immediately noticeable on one ST-35 amplifier. The somewhat marginal Dynaco power transformer now runs much cooler! This, in theory, may result in slightly better B+ regulation for the amp. While the cost of building this "outboard" heavily filtered and regulated supply, was not cheap, I believe it to be less costly than to build, or modify, the filament supplies in each individual unit. The main disadvantage is, of course, that wiring must be run from the outboard supply to each individual unit that it powers. On the other hand, it's easy to implement filament pre-heating prior to the application of high voltage.
I used a transformer made by Hammond. They have a very large selection of filament transformers, and I believe, but am not certain, that they distribute their products internationally.

 

[harwoodspark]

There is another advantage of course. You can warm your amps up before you switch on the HT which will give your valves the chance of a long and happy life. Si.

 

[SY]

Do you have any recommendation for these transformers ?

Surplus.

 

[dejanm]

I have found (up to now) two main sources for these transformers. One is PartConnex (Canada) where I can order Hammond. The other possibility is DigiKey (US) where I can order Tamura. The prices are very similar ... Which way to go ?

 

[zigzagflux]

If they are both dual bobbin, go for the cheaper one.

 

[kevinkr]

I'd try something more local to you than the USA or Canada, Hammond has distribution in the UK and perhaps elsewhere in Europe - check their website.

Farnell in the UK probably has lots of transformers to choose from too.

There are several vendors in Germany that make custom power transformers. Perhaps some European forum members could chime in here with recommendations?

Shipping commodity transformers (there is nothing special to recommend these) from the US or Canada is going to add enough to the cost that you could do better finding a more local source - may save you some money.

 

[dejanm]

Well, meanwhile I did some homework, so it maybe that what I have found out is also interesting for somebody else ...

First of all Kevin was right - transport costs from US to Europe (FEDEX) even for two small transformers are around $50, which is more than the cost of the transformers itselves.

There is only one US distributor that is prepared to send Tamura transformers to Europe (Mouser) without quote limit (between $150 and $250). Tamura does not have sellers in Europe (not for small quantities).

For these reasons I had to look elsewhere -> Hammond. Distribution of Hammond transformers is much better supported in Europe and it is much easier to find them. The prices are considerably higher than in US.

So at the end, I decided to go for Hammond 266L12 model which can be bought in Italy:

http://www.audiokit.it/ITAENG/Trasformatori/Hammond/PowerHam.htm

I must admit that Tamura PF24-12 made much better impression (on the pictures at least) than this Hammond (and it is cheaper), but this unit has two bobines (somebody recommended it) and it fits electricaly nicely to my requirements.

So thanks to everybody who took part in this discussion and helped me to make my decision ...

Regards
Dejan

 

[Bruno66]

I need a filament transformer for the rectifier in a choke loaded supply with 1100VDC out (1200-0-1200Vrms transformer). I will use 6D22S rectifier.

I am considering the Hammond 266 series but they are hippt tested at 2000Vrms. Is this enough or will I burn the transformer?

 

[lhgin]

I did make some comparisons with the different versions of amplifier I made in the past. One guy did make a request to have warm-up option and therefore the separate trannies.

I find that it only make a difference if you are planning to use DC for the filaments where the bridge rectifier is making a lot of noise being back coupled to the HV / B+ voltage rail.

If it is all AC filaments, and if the power transformer is made correctly to have temperature rise considered, the difference is very minimal.

With separate B+ / filament transformers, I usually add a CMC filter at the filament transformers to lower the coupled noise between transformers. It would be better if both the transformers have electrostatic shield.

My 2 cents.

Ken