vintageHIWATTconvention.com

... it still has a decent amount of preamp gain due to the different resistor/cap values compared with the earlier versions. Ah, yes, I see this now. 4-input V1 cathode = 2k2/47n for the Brilliant, and 2k2 for the Normal 2-input V1 cathode - 1k6/150uF (tied) 4-input V3 -> V4 (PI) coupling cap = 22n...

Thanks for posting those links. I've looked into the matter further, and you are correct about the cascaded preamp of the Canadian spec DR105. In addition to removing the variable voltage input facility, the Canadian distributor made a very simple mod that increased the gain of the input section. Th...

After having a closer look at the photos, I believe you are correct about the amps. The Hiwatts appear to be 2-input models with an additional jack in the lower left corner of the panel, placed right through the 'Bright' label. That suggests a second jack was added to the Bright channel, which is wh...

A half watt pot is sufficient. Not much current is conducted through the bias circuit.

A 1 Meg pot is what I use, is easier to find, and works well. A 2 Meg pot may give you 1V of additional range, so it's a small difference.

Here in France we've got 230V so I set my Hiwatt on 240V. Does it mean we have less problems here in Europe with vintage Hiwatts than in the US? Correct. It means the voltages inside your amp should agree with the original circuit diagram. What kind of good measurements tools (bias probes, etc...) ...

Thanks Ted for your detailed reply. I'm still a bit confused on how I should proceed to adjust the bias. As I'm french, I'm not really familiar with the english technical words. The mod seems simple enough to install myself but maybe I should speak with a tech here about biasing. Yes Matthias, I su...

If I were building a clone amp from scratch, I might consider a redesigned bias circuit (as per Mark's suggestions). With an original Hylight era amp, I can vouch for the solution I provided as being non-invasive, effective, and reliable. Do not make the assumption that using original production tub...

Yes, it should work just the same.

If I remember correctly, the maximum bias voltage is around -34-35V, which is almost all the transformer delivers. I do not remember the opposite end of the range, but it is unimportant.

Pinus wrote: Plat Voltage : 460v
Grid bias Voltage: -38v
bias current for each tube: 41.5 mA

This appears to be correct.

Enjoy.

I haven't tried Old School Dave's proposed modification. It appears as though one can use a small trim pot, but two additional resistors are required. I don't know anything about its range of adjustment. The procedure I described is simple, easily reversible, stable, and effective. This is the same ...

The regular SED EL34s are good. As for the Black Sable versions, they reduce the high frequencies, and many do not like them as much as the regular SD EL34s. I would not buy them - especially not at that price.

Another thing that helps is to ask the tube seller to send a set that is selected for low idle current. It won't fix the issue, but it will ensure the tubes can be biased comfortably. In my particular situation, I can bias the tubes to around 34ma, but I have found it sounds audibly better when bias...

I don't understand how to change the Power Tubes without set the bias, there are some kit already matched for this amp? which bias current for the tubes? It is very easy to make the bias adjustable with one small 1-2 Meg potentiometer, as I did here: http://www.vintagehiwattconvention.com/forum/vie...

I did the same thing:
viewtopic.php?f=2&t=1378

My amp seems to be running fine with 42ma - certainly a heckuva lot better than 60ma!