Transformers, do they all "sound" different?

[Blues Hound]

I recently completed my second amp project, converted an 83' Fender Concert II, PT is 018302, OT is 01834 and the Choke is P-CF22699, into a Komet Clone (thanks to Allyn for all the help), but it just doesn't seem to have the same tone, and it sounds very good, notes bloom good clarity, will the trannnies make a big difference in tone? Here are a cople of pictures:

Steve

[Blues Hound]

Preamp Board:

[David Root]

You have it right. Especially the OT. #1 is the primary impedance.

All of Ken Fischer's designs that I've seen use relatively high Zpri impedances, relative to Fender/Marshall/Hiwatt, for instance. Other things being equal, this generally reduces output but also does nice harmonic stuff to the tone. He is also credited with his transformers having particularly good midrange tone. I'm no expert on transformer design and don't know how that is achieved.

PTs are important too. Depending on what you're trying to achieve you may want to oversize, undersize, or not. After all, an amplifier is just a DC power supply modulated by an AC signal. It's important to balance smoothing and cap values. Too much filter capacity can be as bad as too little, there is a happy medium, which is dependent on your design (this is where it gets a bit more complex).

For example, if you're building a '50s blues machine, you might lean towards a smaller (lower VA) PT, perhaps with a choke feed to the plates (very unusual these days) and relatively low cap values to keep a looser tone in the bass.

For a 4-stage hi-gain design with SS rectification, you would want higher cap values at the power end and a relatively high Henry choke feed on the screens, above 10H say, with Marshall-type cap values further back to control the low end.

Personally, I tend toward the higher Henry screen choke and then really lighten up on filter cap values towards the first stage. YMMV. PI caps can vary between 10 and 30 uF, with 20 uF a common choice. In OTs I am tending to higher Z pri but also oversizing ( i.e. using a higher bandwidth design at rated power) to improve bass response. I also now calculate the VA of my rated output and match that to the PT's VA rating for the HT power supply. (You can also do that calculation the other way around. See TUT 2 and TUT 5).

[Blues Hound]

David,

Thanks for the information, that is what I was looking for...the choke I am using is for a Super Reverb, the PT and OT are pertty the same ones that can be used for a Super Reverb, I will have to look up the VA for the PT and the Henry's for the Choke. I have a smaller choke from the Concert II and was thinking of trying that to see what the difference in tone would be...I see that for the Dumble clones the BOM calls for a Marshall PT and a Fender OT, might have to try to build one.

Just re-did the peramp board and moved the filter caps to inside the chassis. I will post some new pictures later today.

I am trying to decide on what I want to build next...leaning towards a JTM 45 or a 50 watt Marshall clone...I do really enjoy building amps.

Steve

[jaysg]

If the OT = 01834 is the stock one in the Concert then it has a less than righteous output distortion tone. If you're not running it that hard, then it's got a decent enough fender clean tone. If that's a replacement from a good vendor, then it should sound fine, but not match the Komet too well.

[Blues Hound]

Re-worked insides of Chassis:

[Blues Hound]

Jaysg,

It is the original OT for the Concert II, will the Hyborer 11451-1 for the TW clone work better? I am going to have to replace the OT with a better match for the amp.

Steve

[jaysg]

It is the original OT for the Concert II, will the Hyborer 11451-1 for the TW clone work better?

Talk to Allyn about it. I replaced mine with one of Dave Allen's pieces, but I'm using it for an ODS with 6L6's. The BF'd clean channel cranked is great.

[Elcabong]

You have it right. Especially the OT. #1 is the primary impedance.

All of Ken Fischer's designs that I've seen use relatively high Zpri impedances, relative to Fender/Marshall/Hiwatt, for instance. Other things being equal, this generally reduces output but also does nice harmonic stuff to the tone. He is also credited with his transformers having particularly good midrange tone. I'm no expert on transformer design and don't know how that is achieved.

I have read that elsewhere too, I mean the part about the reduced output. But I do not understand how it happens. The higher primary load will transfer into a little more voltage and less current but intuitively, I would think that the power would stay the same.

I completed a JTM45 lately and tried both the 6.6k and 8.8k primaries. I prefer the higher impedance and it does translate into a little less power but a sweeter sound to my ears.

[Blues Hound]

Elcabong,

That is interesting, when I built my TW clone, my friend built one at the same time, I used the 5.2K tap and he used the 6.6k tap of the OT and they both sonud great, just different...Billy was thinking of putting a switch to go from 5.2K to 6.6K, but I do not know if he did it.

Steve

[Elcabong]

Steve,

I also experimented with different impedances on my TW clone. I finally decided to use the 5.2k tap; just my preference.

Here is an interesting article I found on load impedance even if it is for Class A amplifier.

http://www.obsoleteelectronics.com/Tran ... edance.htm

[David Root]

I have seen that article before. It's fine as far as it goes, but it doesn't specifically address push-pull operation. The general relationship between Po, even/odd harmonic distortion % and Zpri is the same in A-B P-P pentode mode however.

I have recently been reviewing such curves for 6550 and KT77s for my next build, and the Vp vs Ip curves too. My major problem is the mfrs. never published plate curves for very high screen voltages, because it wasn't "good practice" to operate that way in the '50s (except for Ultra-linear, which doesn't sound great in MI amp designs). I plan to run the plate at 450V and the screen at 447V, which is pushing both tube types.

The other thing I didn't totally agree with is the comment in page 2 about 3800 ohms being " for these operating voltages and this tube, ...., probably the optimum load." For max. power at lowest total distortion, yes. This is where individual tastes come in. That graph shows 2nd harmonic at zero at 3800 ohms., but 3rd harmonic at 7%. It's true that total 2nd & 3rd is minimum at about 3800 ohms, but zero 2nd and 7% 3rd would not be optimum to my ears! I would probably go for 2200 ohms, 10% THD but 8% of it is 2nd harmonic! But at 2200 ohms, power is only 5W vs. 14W at 3800 ohms (this is a single tube here).

So you pays yer money and you takes yer choice! At least at whatever Vp and Vs that graph was done at. Increasing both Vp and Vs relative to Vp will give much more power across the board, which is what I'm looking at doing.

[Blues Hound]

This is going to be interesting, has anyone tried the DYANCO OT's, either the A-420 or the A-470? At $27.00 I am thinking of givin em' a whril...

[dobbhill]

Where are you buying these Dyna trannies?!!!

[sportster4eva]

Where are you buying these Dyna trannies?!!!

Where are you buying these Dyna trannies?!!!