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 Post subject: Heathkit tube amp
PostPosted: Jun Thu 27, 2019 7:15 pm 
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Joined: Mar Tue 25, 2014 8:36 pm
Posts: 40
I just bought a Heathkit W4 AM. I want to use a Weathers preamp with it. Do I have to assemble some sort of a shunt to plug into that tube socket next to the audio input jack?

Thanks,

Roland


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 Post subject: Re: Heathkit tube amp
PostPosted: Jun Fri 28, 2019 12:46 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 20573
Location: Utica, NY 13502 (USA)
The octal socket connections are used to power a matching preamp whose power switch is also used to turn on the amp. You can simply solder a jumper between lugs 6 and 7 or mount toggle switch connected to those lugs. You can insert an octal plug with pins 6 and 7 jumpered if you want to go to that trouble. Some preamps have switched AC sockets for turning on the amp.

Attachment:
Heathkit W4AM Preanp Socket.JPG
Heathkit W4AM Preanp Socket.JPG [ 51.04 KiB | Viewed 942 times ]


Dave


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 Post subject: Re: Heathkit tube amp
PostPosted: Jul Mon 01, 2019 5:44 pm 
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Joined: Mar Tue 25, 2014 8:36 pm
Posts: 40
Thank you.


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 Post subject: Re: Heathkit tube amp
PostPosted: Jul Mon 15, 2019 5:54 pm 
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Joined: Mar Tue 25, 2014 8:36 pm
Posts: 40
I tried the amp this weekend and it works without any jumper, but fairly low as seller stated. I'll try using a preamp next time. Why do I need that jumper?

Thanks,

Roland


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 Post subject: Re: Heathkit tube amp
PostPosted: Jul Mon 15, 2019 10:29 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Utica, NY 13502 (USA)
If the socket is wired as shown above, the transformer will not get power. Maybe someone wired the socket differently, (i.e. removed the wire from pin 6 and connected to pin 7 or vice versa). When buying a kit built by someone other than yourself, you never know what might have been done.

Dave


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 Post subject: Re: Heathkit tube amp
PostPosted: Jul Mon 15, 2019 10:55 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Fernandina Beach, FL
Dave Doughty wrote:
If the socket is wired as shown above, the transformer will not get power. Maybe someone wired the socket differently, (i.e. removed the wire from pin 6 and connected to pin 7 or vice versa). When buying a kit built by someone other than yourself, you never know what might have been done.

Dave

EXACTLY what Dave has said. I have refrained from comment but felt the same way...

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Don


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 Post subject: Re: Heathkit tube amp
PostPosted: Jul Tue 16, 2019 7:14 pm 
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Joined: Mar Tue 25, 2014 8:36 pm
Posts: 40
Would changing the socket wires be either a "work or don't work" situation? The amp works but fairly low. I intend to try a pre amp next and see how loud it works.

Thanks to all,

Roland


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 Post subject: Re: Heathkit tube amp
PostPosted: Jul Tue 16, 2019 10:18 pm 
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Location: Utica, NY 13502 (USA)
As I said before, the connections on that octal socket are for switching the AC power to the amp and to provide filament and B+ voltage for a matching preamp.

The power wiring scheme at that socket has nothing to do with the low level you are experiencing.. What are you using as an input source?

Basic tube amps were designed to be driven by the relatively high impedance, high voltage output of a tube preamp or a solid state preamp designed to drive a tube or transistor amp. If you are using one of todays audio products (such as an MP3 player), it will have a relatively low impedance, low voltage output which is insufficient for a basic tube amplifier such as the Heathkit W4AM. I've found this to be the case with the audio from my HP desktop computer and, especially, my android tablet used for internet music streaming. The simple workaround is to use a low-to-high impedance audio transformer which results in a better match for tube amplifiers and radios.

According to the manual, a 1-volt RMS input will produce about 3-watts output from the W4AM. Typical modern device output sources are usually far less than that. Here is the manual for your amp.

http://www.tubebooks.org/file_downloads ... Manual.pdf

Dave


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 Post subject: Re: Heathkit tube amp
PostPosted: Jul Tue 16, 2019 10:36 pm 
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Joined: Mar Tue 25, 2014 8:36 pm
Posts: 40
Dave:

Thank you for the manual link. I am using an old Weathers cartridge. I don't think it's a crystal type. Eventually I want to use a Weathers FM cartridge with the oscillator and Weathers preamp. We'll see how that works.

Roland


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 Post subject: Re: Heathkit tube amp
PostPosted: Jul Wed 17, 2019 12:24 am 
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Location: Utica, NY 13502 (USA)
tvinbasement wrote:
I am using an old Weathers cartridge. I don't think it's a crystal type.
I suspect that is likely the problem with low volume level from your Heathkit basic amp. It was never designed to be driven directly from a phono cartridge. A high output crystal cartridge might drive it to a higher level, however.

What model is your Weathers cartridge and preamp?

Dave


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 Post subject: Re: Heathkit tube amp
PostPosted: Jul Tue 23, 2019 5:21 pm 
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Joined: Mar Tue 25, 2014 8:36 pm
Posts: 40
The cartridge is the FM capacitor kind, I don't have a model number. The oscillator is the P-620.


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