Looks like my PT is toast.
Does anyone know the specs or know of a good substitution for Eico HF-89 PT?
I'll start crunching numbers from tube spec sheets working back from specified plate voltage, but would be nice if I could find the actual specs!
These have HV, bias V and 6.3v filament, SS rectifer and power 4-EL34's 2-6SN7GTS and 1-12AX7
Does anyone know the specs or know of a good substitution for Eico HF-89 PT?
I'll start crunching numbers from tube spec sheets working back from specified plate voltage, but would be nice if I could find the actual specs!
These have HV, bias V and 6.3v filament, SS rectifer and power 4-EL34's 2-6SN7GTS and 1-12AX7
According to the post below, the specs according to Sams were:
170V @ 0.9A
6.3V @ 7.6A
75V for bias
The poster also mentions that Heyboer had wound custom transformers for the HF87/89. This implies the HF89 and 87 uses the same power transformer (I just checked the service manuals and the power transformer part no listed is indeed the same for both HF87 and 89, i.e. #30031). If needed, I have an HF87 and could measure the voltages for you. Let me know.
https://www.diyaudio.com/forums/swap-meet/361914-tube-iron-sale.html#post6384123
170V @ 0.9A
6.3V @ 7.6A
75V for bias
The poster also mentions that Heyboer had wound custom transformers for the HF87/89. This implies the HF89 and 87 uses the same power transformer (I just checked the service manuals and the power transformer part no listed is indeed the same for both HF87 and 89, i.e. #30031). If needed, I have an HF87 and could measure the voltages for you. Let me know.
https://www.diyaudio.com/forums/swap-meet/361914-tube-iron-sale.html#post6384123
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Well I'll be darned. Looks like my TF is OK after all. I thought that based on the Eico list of voltages and resistances, with plate voltage at 478V, that the TF output I was seeing was inadequate VAC at the transformer.
But based on this 170V spec you found, I searched around and found a PS schematic from Dave Gillaspie with power supply voltages for HF87 conversion. It shows 187VAC, exactly what my tranny is reading. His B+ is 443.
Voltage doubler.
I put the cart before the horse. Should have scrutinized the schematic.
Apologies.
But based on this 170V spec you found, I searched around and found a PS schematic from Dave Gillaspie with power supply voltages for HF87 conversion. It shows 187VAC, exactly what my tranny is reading. His B+ is 443.
Voltage doubler.
I put the cart before the horse. Should have scrutinized the schematic.
Apologies.
When I rebuilt my HF87, the power supply transformer was toast. I just used an off the shelf Hammond, and removed the voltage doubler circuit entirely. I don't have the model handy, but for a 5 tube amp of this size, everyone makes something. I've used Edcor on many of my own builds with great success too.
Audio Engineering - EICO HF87 Restoration Project by Sean Rose
Audio Engineering - EICO HF87 Restoration Project by Sean Rose
You made it all pretty!
Thanks for the "chuck the voltage doubler" outlook! I am all for simplifying PS design.
Did you retain the 87's cathode bias scheme?
Thank you. I did, but I typically do something unusual. I have 2 switches in the circuit that switch the bias from about 1/3 to full dissipation, and then El34/6L6 vs 6550/KT88. So... when I rewired this, you can drop in either tube set. Low bias is for like watching TV and to prolong tube life (I am skeptical this works though in practice, as modern tubes are designed to fail with heater burnout). I used one of the back previous 110V sockets to add another switch that allows you you to select 6550 instead of EL34. I have built many amps of self bias and fixed bias over the years, I have yet to find a best, both have merit... but for simplicity of building and if max power is not your end target, self bias is a great thing. It would def be my choice for a first build.. or if you don't feel comfy on your own. I would recommend doing what I did so you can tube swap and try different tube families.