Eico HF-20 amplifier repair question

script56

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I have a eico hf 20 pair of amps. I plugged one in with variac and ok. May need new caps. The other is later version with fuse. I installed new fuse and powered on. 10 second smoke is coming from power transformer. I powered off. Transformer was still warm 1 hr later. Will this possibly still be ok to use or is it for sure in need of replacement.

Also does anyone have a spare to sel?
 
Not a good sign on two accounts -- smoke from the transformer is almost surely an indication that windings inside the transformer are compromised and will need to be replaced, but also, why didn't the fuse blow? What size fuse was installed when this happened?

Dave
 
That's what I'm wondering why fuse didn't blow. 15v 250 I believe. I put in correct fuse according to fuse cap.
 
Well maybe it is an aftermarket fuse because on the fuse mount it reads 15 V maybe I can find a replacement transformer somewhere.
 
I have a HF20 so I will be watching this thread. I have seen post where people change out the power trans and maybe the output tubes and get 50 Watts out of one. I would love to have a HF52 some day . I believe the output trans 32004 is a real winner. A friend of mine has a pair of HF22's with that OPT and I was impressed to say say least. Started down the path of tubes and put Eico on my radar. Good luck to you.
 
If I may, at the primary impedance level that the 32004 transformer represents (7600 ohms plate-to-plate), it is not possible to get anywhere near 50 watts through or out of those transformers, except maybe at mid frequencies only. With respect to producing a flat 20 Hz to 20 kHz power band, about the most these transformers are good for with typical B+ voltages and even EL34 output tubes is 28 watts RMS at 20 Hz. This paring was really a compromised choice to use in the HF-35, as the power band of that amplifier falls off notably on the low end -- again, down to the above mentioned power level from a mid frequency power output of about 34 watts. Of the HF-20/22/35/50/52/60 series of amplifiers, the HF-35 is the only model to have a reduced LF power response.

This is hardly to say that the 32004 is a poor transformer -- in fact, quite the contrary. When used with 6L6 class tubes with cathode bias and a 465 volt B+ supply, they will produce an absolutely flat power band from 20 Hz to 20 kHz, at a maximum power output of 22 watts RMS, and can do so with very low distortion.

The 32007 transformer, as used in the HF-50/52 is also an excellent transformer (lower primary impedance), but requires a bigger power transformer than the HF-20/22 employs to produce the power it is capable of handling. As good as this transformer is however, it is bested by those in the HF-89/A, but even these are not as good as the HF-60's Acrosound TO-330 transformers, which even today remain a standard to be beat.

Dave
 
Fortunately there are plenty of folks who are using the 32004's in some other build and have the original power iron taking up space in the spares pile...:)
cheers,
Douglas
 
Script -- that is likely the rating for the fuse holder itself. That is, the maximum current it can handle. The unit itself should be fused with a 2A fuse. As knockbill pointed out, with a 15A fuse installed, that is why it didn't blow.

Dave
 
If I may, at the primary impedance level that the 32004 transformer represents (7600 ohms plate-to-plate), it is not possible to get anywhere near 50 watts through or out of those transformers, except maybe at mid frequencies only. With respect to producing a flat 20 Hz to 20 kHz power band, about the most these transformers are good for with typical B+ voltages and even EL34 output tubes is 28 watts RMS at 20 Hz. This paring was really a compromised choice to use in the HF-35, as the power band of that amplifier falls off notably on the low end -- again, down to the above mentioned power level from a mid frequency power output of about 34 watts. Of the HF-20/22/35/50/52/60 series of amplifiers, the HF-35 is the only model to have a reduced LF power response.

This is hardly to say that the 32004 is a poor transformer -- in fact, quite the contrary. When used with 6L6 class tubes with cathode bias and a 465 volt B+ supply, they will produce an absolutely flat power band from 20 Hz to 20 kHz, at a maximum power output of 22 watts RMS, and can do so with very low distortion.

The 32007 transformer, as used in the HF-50/52 is also an excellent transformer (lower primary impedance), but requires a bigger power transformer than the HF-20/22 employs to produce the power it is capable of handling. As good as this transformer is however, it is bested by those in the HF-89/A, but even these are not as good as the HF-60's Acrosound TO-330 transformers, which even today remain a standard to be beat.

Dave

As I have mentioned before, I still wonder what would happen, if an HF35 was converted to fixed bias, and used with 4 ohm speakers on the 8 ohm tap (or 8 ohm speakers on the 16 ohm tap)...

If it worked with the Eico ST70 (halving the secondary load impedance)- it might work here too???

The 3800 ohm loading (in fixed bias) would be fine for an EL34. It's a bit lower than the 4300 ohm load of a Dynaco A470 (ST70 output), but not enough to put it out of the ballpark...

Also, in fixed bias, the idle current could be lower (reducing the average load on the power transformer)...
 
If I may, at the primary impedance level that the 32004 transformer represents (7600 ohms plate-to-plate), it is not possible to get anywhere near 50 watts through or out of those transformers, except maybe at mid frequencies only. With respect to producing a flat 20 Hz to 20 kHz power band, about the most these transformers are good for with typical B+ voltages and even EL34 output tubes is 28 watts RMS at 20 Hz. This paring was really a compromised choice to use in the HF-35, as the power band of that amplifier falls off notably on the low end -- again, down to the above mentioned power level from a mid frequency power output of about 34 watts. Of the HF-20/22/35/50/52/60 series of amplifiers, the HF-35 is the only model to have a reduced LF power response.

This is hardly to say that the 32004 is a poor transformer -- in fact, quite the contrary. When used with 6L6 class tubes with cathode bias and a 465 volt B+ supply, they will produce an absolutely flat power band from 20 Hz to 20 kHz, at a maximum power output of 22 watts RMS, and can do so with very low distortion.

The 32007 transformer, as used in the HF-50/52 is also an excellent transformer (lower primary impedance), but requires a bigger power transformer than the HF-20/22 employs to produce the power it is capable of handling. As good as this transformer is however, it is bested by those in the HF-89/A, but even these are not as good as the HF-60's Acrosound TO-330 transformers, which even today remain a standard to be beat.

Dave
I have a eico hf 20 pair of amps. I plugged one in with variac and ok. May need new caps. The other is later version with fuse. I installed new fuse and powered on. 10 second smoke is coming from power transformer. I powered off. Transformer was still warm 1 hr later. Will this possibly still be ok to use or is it for sure in need of replacement.

Also does anyone have a spare to sel?
I have a eico hf 20 pair of amps. I plugged one in with variac and ok. May need new caps. The other is later version with fuse. I installed new fuse and powered on. 10 second smoke is coming from power transformer. I powered off. Transformer was still warm 1 hr later. Will this possibly still be ok to use or is it for sure in need of replacement.

Also does anyone have a spare to sel?
Is it OK to use 6L6GC with the HF-20. Getting a plate current of about 45ma? Thanks!
 
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