UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Bestone TRF

egerton · 25th Jul 2018, 11:04 am

I've started a new thread as I've moved on to the power up and testing phase on the Bestone 20 TFR I am restoring. The earlier thread here: https://www.vintage-radio.net/forum/...d.php?t=147542 has history of how I got to this point. Learned a lot... thanks guys. Anyway I had established the series heater chain had correct voltages and the rectifier seemed ok - now time to connect HT to the audio stage ONLY.

Got a crackle and hum from speaker when grid touched! We are go! ..but the HT has collapsed somewhat!

Noticed though there was an ongoing random crackling sound - like a noisy component breaking down even when I don't touch the grid. This stops completely when I ground the grid. Is that static build up on grid or noisy valve or component?

Switched off and ponder this test. Previously measured HT (no load) with i/p supply (100w bulb) 121v giving C2 131v, C3 125v.

With HT to audio stage and speaker field coil connected i/p supply (needed 110w bulb) to give 115v a/c supply and C2 91V, C3 86V. Is this enough?

I propose to measure the HT current next. As a check, cathode resistor R3 had 11V across it. Calc. cathode current as 11/650 = 17mA looks reasonable as a quiescent current?

Any comment greatly welcomed, at least I've heard a sound out of the set

Paul

25th Jul 2018, 11:04 am	#1
egerton Pentode Join Date: May 2018 Location: Beverley, East Riding Posts: 110	Bestone TRF - power up and audio stage testing I've started a new thread as I've moved on to the power up and testing phase on the Bestone 20 TFR I am restoring. The earlier thread here: https://www.vintage-radio.net/forum/...d.php?t=147542 has history of how I got to this point. Learned a lot... thanks guys. Anyway I had established the series heater chain had correct voltages and the rectifier seemed ok - now time to connect HT to the audio stage ONLY. Got a crackle and hum from speaker when grid touched! We are go! ..but the HT has collapsed somewhat! Noticed though there was an ongoing random crackling sound - like a noisy component breaking down even when I don't touch the grid. This stops completely when I ground the grid. Is that static build up on grid or noisy valve or component? Switched off and ponder this test. Previously measured HT (no load) with i/p supply (100w bulb) 121v giving C2 131v, C3 125v. With HT to audio stage and speaker field coil connected i/p supply (needed 110w bulb) to give 115v a/c supply and C2 91V, C3 86V. Is this enough? I propose to measure the HT current next. As a check, cathode resistor R3 had 11V across it. Calc. cathode current as 11/650 = 17mA looks reasonable as a quiescent current? Any comment greatly welcomed, at least I've heard a sound out of the set Paul