hammomd 370HX issues

[sloblues]

hi all,
so i just installed a new Hammond 370HX. having never used a universal power tran before I have issues and am hoping one of you members might set me on the right path.
This 370hx has primary wires for 100,110,120,220,240 VAC ..... my voltage (in Wash DC area) is 122.4VAC so it makes sense to me to use the 120 vac primary. The wiring diagram shows blue and brown as 120vac and 0 vac respectively one half of the primary windings and also a black 120vac and white 0 vac on the 'other half' of the primary. So first I used brown and white for one leg and black and blue for the other side. This yielded 294 VAC to the red wires going to pins 4 and 6 of the rectifier socket. The yellow 5VAC on the recto socket showed 2.9VAC to ground and 5.8VAC across the pins 2/8 ...but when I put in the recto tube (going to use a GZ34 but for testing using an old 5y3) and within 15 seconds the tube start arcing internally .. .... so I switched primary wiring to use only black and white .... then again to use only blue and brown ...either of these two yielded about the same 295 VAC on red wires and 5.4VAC on recto sockets --all three ways arc the recto tubes in about 20 seconds (I tried three diff recto tubes that I l know from other amps I have all work fine) ... Also there are no other tubes installed and OPT is not wired up yet
so as a cartoon I used to watch sez ...could someone kindly "help mister wizard"
thanks!

[DIY_Guy]

You grounded the center tap wire for the 5v, right? Look for mis-wiring on the socket, could be an issue there too. It's gotta be something simple seeing as how it's just the transformer you have hooked up and nothing else.

[MWJB]

Shouldn't the 5VAC CT be connected to main B+?

[sloblues]

Shouldn't the 5VAC CT be connected to main B+?

I don't know MWJB - no wiring sheet came with the tran. Hammomd's website has a wiring diagram but no explanations on when to use the various taps. I grounded the yel/blh striped senter tap for the 5VAC yellow windings ....the socket is brand new eveything is for that matter ... just getting built ...

[MWJB]

Don't ground the yel/blk 5VAC CT

[DIY_Guy]

The yellow/black is for the 6.3v tap. The orange should be for the 5v

[sloblues]

The yellow/black is for the 6.3v tap. The orange should be for the 5v

therein lies my problem the hammomd 300XX series shows what you describe BUT my 370HX is NOT the same on the secondary windings it only has this: 1 violet 50vac for bias tap. one green/yellow CT for 6.3VAC heater windings consisting of two green wires, and one yel/blk CT for the two yellow 5VAC recto heaters. There is no 'second' 5VAC windings that use an Orange CT. I would post the wiring diagram but do not know how.
Maybe I can call Hammomd and get this cleared up .. I was hoping someone here has expereice with this particular tran.

[sloblues]

tried that and got like 60-70VAC on the 5VAC yellow windings i have used several 270xx series hammonds never has one try to fry rectifiers like this multi tap beast....

[DIY_Guy]

therein lies my problem the hammomd 300XX series shows what you describe BUT my 370HX is NOT the same on the secondary windings it only has this: 1 violet 50vac for bias tap. one green/yellow CT for 6.3VAC heater windings consisting of two green wires, and one yel/blk CT for the two yellow 5VAC recto heaters. There is no 'second' 5VAC windings that use an Orange CT. I would post the wiring diagram but do not know how.
Maybe I can call Hammomd and get this cleared up .. I was hoping someone here has expereice with this particular tran.

Hmm they must have made yours differently than what they show on the wiring diagrams. I think your best bet is to call them and find out what is what.

[Ken Moon]

How to connect 370HX

To connect the primaries for 120V:

1. Connect the '120V Blk' and '120V Blu' wires together, and then connect them both to one side of your AC line.

2. Connect the '0V Wht' and '0V Brn' wires together, and then connect them both to the other side of your AC line.



The 6.3V ct secondary has two green wires and one green/yellow wire, which is the ct.

The 5V ct secondary has two yellow wires and one yellow/black wire, which is the ct.

There are lots of ways to connect the secondaries - you can use the 5V ct for your HT output, and in other designs the 5V ct would just be taped off.

The bottom circuit here, from Merlin's Valve Wizard web page, shows an example of using the 5V ct for the HT:



The full page is here:

The Valve Wizard

There are also lots of ways to use the 6.3V ct heater winding, and some are very helpful in reducing hum.

[sloblues]

problem solved!

thanks for all the suggestions and tips, I called Hammond in New York and spoke to a transformer tech ,,great guy super friendly - says a lot to me about Hammond! So the deal is Hammomd added all these taps to accomodate numerous requests they get for "more features" and "more flexibility" .. so Ken was right, although I could use just blk/wht or blue/brn for 120AV primary, using them together is the best way as it uses all the primary winding not just half- thus allowing full current usage. The Yellow/Black "center tap" for the Yellow 5VAC leads is NOT a center tap for 5vac leads, but is B+ that can be sent to a HT rail. In my case I am to tape it off as I do not need additional HT rails.

cheers !

[sloblues]

on second thought .... I see what Ken meant: this if from the url Ken mentioned:

If the rectifier has a directly heated cathode or if the heater is internally connected to the cathode (like the GZ34), then it will need a separate filament supply. If the filament supply has a centre tap then the HT should be taken from there, which will help to reduce HT noise induced by the filament.

Does this mean that instead of taking B+ from pin8 of the recto tube as I usually do, I can use the blk/yel tap instead for B+ and that may be "quieter" than coming off pin8 ?

[Ken Moon]

I used the 5V ct for the HT in the Talon amp, which has a GZ34 rectifier:



It seemed really strange to me also, because the heater windings are so short compared to the full HT windings, but it does seem to work

Can't really say if it's quieter though - I've never built two amps with only that one difference to compare

[loudthud]

There is usually slight imbalance in the HV CT winding of most transformers because it takes a longer piece of wire (more resistance) to wind an equal number of turns on the second half of the winding. This results in a every other ripple pulse being a couple of volts higher than the others. You could fix this by imbalancing what Merlin calls RLim1 and RLim2. You can simply measure the resistance to the CT to get the required resistance and figure out which red wire needs more resistance.

The 5V CT is really intended for directly heated rectifier tubes like the 5Y3 and 5U4. The GZ34 has a cathode so the B+ should be taken from pin 8 and the CT not used.

In most guitar amps the imbalance is not considered significant.

[sloblues]

thanks man , ( like that handle "loud thud" ) so it seems then that pin 8 (for my GZ34's) vice the CT is the best choice for guitar amps needs, although, as Ken's Talon Amp above demonstrates, using the CT works fine also.